Encoding method based on encoding order change and device therefor, and decoding method based on encoding order change and device thprefor

ABSTRACT

Provided is a video decoding method including obtaining split information indicating whether a current block is to be split; and when the split information indicates that the current block is to be split, splitting the current block into at least two lower blocks, obtaining encoding order information indicating an encoding order of the at least two lower blocks of the current block from the bitstream, determining a decoding order of the at least two lower blocks based on the encoding order information, and decoding the at least two lower blocks according to the decoding order.

CROSS-REFERENCE TO THE RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 17/326,986 filed May 21, 2021, which is a continuation of U.S. application Ser. No. 16/467,411, filed Jun. 6, 2019, which claims priority from International Application No. PCT/KR2017/015212, filed on Dec. 21, 2017 and U.S. Provisional Application No. 62/439,178, filed on Dec. 17, 2016, respectively. The entire disclosures of the prior applications are considered part of the disclosure of this continuation application, and are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a video encoding method and a video decoding method, and more particularly, to intra and inter prediction methods for methods and devices for determining encoding and decoding orders of an image.

BACKGROUND ART

When a video of high quality is encoded, a large amount of data is required. However, because a bandwidth available for transmission of the video data is limited, a data rate applied to transmission of the video data may be limited. Therefore, for efficient transmission of video data, there is a need for video data encoding and decoding methods with minimal deterioration in image quality and increased compression rates.

Video data may be compressed by removing spatial redundancies and temporal redundancies between pixels. Because neighboring pixels generally have common characteristics, encoding information of a data unit consisting of pixels is transmitted to remove redundancies between the neighboring pixels.

Pixel values of the pixels included in the data unit are not directly transmitted but information about a method of obtaining the pixel values is transmitted. A prediction method, in which a pixel value that is similar to an original value is predicted, is determined for each data unit, and encoding information about the prediction method is transmitted from an encoder to a decoder. Because a prediction value is not completely equal to the original value, residual data of a difference between the original value and the prediction value is transmitted from the encoder to the decoder.

When prediction is exact, a size of the encoding information for specifying the prediction method is increased but a size of the residual data is decreased. Therefore, the prediction method is determined, in consideration of sizes of the encoding information and the residual data. In particular, a data unit that is split from a picture has various sizes, and in this regard, when a size of the data unit is increased, there is an increased probability that accuracy of prediction is decreased, whereas the size of encoding information is decreased. Thus, a size of a block is determined according to characteristics of a picture.

The prediction method includes intra prediction and inter prediction. The intra prediction is a method of predicting pixels of a block from pixels adjacent to the block. The inter prediction is a method of predicting pixels by referring to pixels of a different picture referred to for a picture including the block. Therefore, spatial redundancy is removed by the intra prediction, and temporal redundancy is removed by the inter prediction.

When the number of prediction methods is increased, an amount of encoding information for indicating the prediction method is increased. Thus, the amount of the encoding information may be decreased by predicting, from a different block, the encoding information to be applied to a block.

Because loss of video data is allowed to the extent that the human eye cannot recognize the loss, residual data may be lossy-compressed according to transformation and quantization processes, and by doing so, an amount of the residual data may be decreased.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided is a video encoding method of determining whether to split a current block and an encoding order of lower blocks, and determining an encoding method according to whether neighboring blocks of the current block have been encoded. Provided is a video decoding method of splitting a current block, determining an encoding order of split lower blocks, and determining an encoding method according to whether neighboring blocks of the current block have been encoded. In addition, a computer-readable recording medium having recorded thereon a program for executing the video encoding method and the video decoding method according to an embodiment on a computer is provided.

Solution to Problem

Provided is a video decoding method including obtaining, from a bitstream, split information indicating whether a current block is to be split; when the split information indicates that the current block is not to be split, decoding the current block according to encoding information about the current block; and when the split information indicates that the current block is to be split, splitting the current block into at least two lower blocks, obtaining encoding order information indicating an encoding order of the at least two lower blocks of the current block from the bitstream, determining a decoding order of the at least two lower blocks based on the encoding order information, and decoding the at least two lower blocks according to the decoding order.

Provided is a video decoding device including a block splitter configured to split a current block into at least two lower blocks when split information indicating whether the current block is to be split indicates that the current block is to be split; an encoding order determiner configured to determine, when the current block is split into the at least two lower blocks, a decoding order of the at least two lower blocks being based on encoding order information indicating an encoding order of the at least two lower blocks; a prediction method determiner configured to determine a prediction method for the current block when the split information indicates that the current block is not to be split; and a decoder configured to reconstruct the current block according to a result of prediction by the prediction method.

Provided is a video encoding method including splitting a current block into at least two lower blocks; determining, according to a result of the splitting of the current block, whether to split the current block, and generating split information indicating whether the current block is to be split; according to coding efficiency of the current block, determining an encoding order of the at least two lower blocks of the current block, and generating encoding order information indicating the encoding order of the at least two lower blocks; and outputting a bitstream including the split information and the encoding order information.

Provided is a video encoding device including an encoding information generator configured to split a current block into at least two lower blocks; determine, according to a result of the splitting of the current block, whether to split the current block; generate split information indicating whether the current block is to be split, according to coding efficiency of the current block; determine an encoding order of the at least two lower blocks of the current block; and generate encoding order information indicating the encoding order of the at least two lower blocks; and an output unit configured to output a bitstream including the split information and the encoding order information.

Provided is a non-transitory computer-readable recording medium having recorded thereon a program for performing the video encoding method and the video decoding method.

The technical problems of the present disclosure are not limited to the aforementioned technical features, and other unstated technical problems may be inferred from embodiments below.

Advantageous Effects of Disclosure

Whether to split a current block and an encoding order of a lower block are determined, and a prediction method for the lower block is determined according to the encoding order of the lower block, so that coding efficiency of an image is increased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A illustrates a block diagram of an image encoding device based on coding units according to a tree structure, according to an embodiment of the present disclosure.

FIG. 1B illustrates a block diagram of an image decoding device based on coding units according to a tree structure, according to an embodiment.

FIG. 2 illustrates a process of determining at least one coding unit by splitting a current coding unit, according to an embodiment.

FIG. 3 illustrates a process of determining at least one coding unit by splitting a coding unit having a non-square shape, according to an embodiment.

FIG. 4 illustrates a process of splitting a coding unit based on at least one of block shape information and split shape information, according to an embodiment.

FIG. 5 illustrates a method of determining a predetermined coding unit from among an odd number of coding units, according to an embodiment.

FIG. 6 illustrates an order in which a plurality of coding units are processed when a current coding unit is split and thus the plurality of coding units are determined, according to an embodiment.

FIG. 7 illustrates a process of determining a current coding unit to be split into an odd number of coding units when coding units are unable to be processed in a predetermined order, according to an embodiment.

FIG. 8 illustrates a process of determining at least one coding unit when a first coding unit is split, according to an embodiment.

FIG. 9 illustrates that, when a second coding unit having a non-square shape, which is determined when a first coding unit is split, satisfies a predetermined condition, a shape of the second coding unit that is splittable is limited, according to an embodiment.

FIG. 10 illustrates a process of splitting a coding unit having a square shape when split shape information indicates that the coding unit is not to be split into four coding units having square shapes, according to an embodiment.

FIG. 11 illustrates that a processing order between a plurality of coding units may be changed according to a process of splitting a coding unit, according to an embodiment.

FIG. 12 illustrates a process of determining a depth of a coding unit as a shape and size of the coding unit change, when the coding unit is recursively split and thus a plurality of coding units are determined, according to an embodiment.

FIG. 13 illustrates a depth determinable according to shapes and sizes of coding units, and a part index (PID) for distinguishing between the coding units, according to an embodiment.

FIG. 14 illustrates that a plurality of coding units are determined according to a plurality of predetermined data units included in a picture, according to an embodiment.

FIG. 15 illustrates a processing block that is a criterion in determining a determining order of a reference coding unit included in a picture, according to an embodiment.

FIG. 16 illustrates a video decoding device involving splitting a current block and determining an encoding order of split lower blocks, according to an embodiment.

FIGS. 17A to 17C illustrate a default encoding order according to an embodiment.

FIGS. 18A and 18B respectively illustrate a case in which a coding unit is encoded in a forward direction and a case in which a coding unit is encoded in a backward direction.

FIG. 19 illustrates a tree structure of a largest coding unit for describing an encoding order of a largest coding unit and coding units included in the largest coding unit.

FIGS. 20A and 20B illustrate how an encoding order of at least three blocks arranged in a vertical or horizontal direction is changed according to an encoding order flag.

FIGS. 21A and 21B illustrate a method of transforming a current block when a right block, not a left block, of the current block has been decoded prior to the current block.

FIG. 22 illustrates a method of determining a most probable mode (MPM) of a current block.

FIG. 23 is a diagram for describing smoothing with respect to reference pixels to be referred to in intra prediction with respect to a current block.

FIGS. 24A and 24B illustrate a method of determining a residual block according to horizontal differential pulse-code modulation (DPCM).

FIG. 25 illustrates a range of neighboring samples necessary to determine an illumination coefficient with respect to illumination compensation.

FIGS. 26A to 26C illustrate a method of predicting a current block according to a position dependent intra prediction combination (PDPC) mode.

FIG. 27 illustrates a video decoding method according to an embodiment involving splitting a current block and determining an encoding order of split lower blocks.

FIG. 28 illustrates a video encoding device according to an embodiment involving splitting a current block and determining an encoding order of split lower blocks.

FIG. 29 illustrates a video encoding method according to an embodiment involving splitting a current block and determining an encoding order of split lower blocks.

BEST MODE

Provided is a video decoding method including obtaining, from a bitstream, split information indicating whether a current block is to be split; when the split information indicates that the current block is not to be split, decoding the current block based on encoding information about the current block; and when the split information indicates that the current block is to be split, splitting the current block into at least two lower blocks, obtaining encoding order information indicating an encoding order of the at least two lower blocks of the current block from the bitstream, determining a decoding order of the at least two lower blocks based on the encoding order information, and decoding the at least two lower blocks according to the decoding order.

Provided is a video decoding device including a block splitter configured to split a current block into at least two lower blocks when split information indicating whether the current block is to be split indicates that the current block is to be split; an encoding order determiner configured to determine, when the current block is split into the at least two lower blocks, a decoding order of the at least two lower blocks based on encoding order information indicating an encoding order of the at least two lower blocks; a prediction method determiner configured to determine a prediction method for the current block when the split information indicates that the current block is not to be split; and a decoder configured to reconstruct the current block according to a result of prediction by the prediction method.

Mode of Disclosure

Advantages and features of embodiments and methods of accomplishing the same may be understood more readily by reference to the following detailed descriptions of the embodiments and the accompanying drawings. In this regard, the present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the present embodiments to one of ordinary skill in the art.

Hereinafter, the terms used in the specification will be briefly defined, and the embodiments will be described in detail.

All terms including descriptive or technical terms which are used herein should be construed as having meanings that are obvious to one of ordinary skill in the art. However, the terms may have different meanings according to the intention of one of ordinary skill in the art, precedent cases, or the appearance of new technologies. Also, some terms may be arbitrarily selected by the applicant, and in this case, the meaning of the selected terms will be described in detail in the detailed descriptions of the disclosure. Thus, the terms used herein have to be defined based on the meaning of the terms together with the descriptions throughout the specification.

An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context.

Throughout the specification, when a part “includes” or “comprises” an element, unless there is a particular description contrary thereto, the part can further include other elements, not excluding the other elements. Also, the term “unit” used in the specification means a software component or hardware component such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), and performs specific functions. However, the term “unit” is not limited to software or hardware. The “unit” may be formed so as to be in an addressable storage medium, or may be formed so as to operate one or more processors. Thus, for example, the term “unit” may refer to components such as software components, object-oriented software components, class components, and task components, and may include processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, micro codes, circuits, data, a database, data structures, tables, arrays, variables, or the like. A function provided by the components and “units” may be associated with the smaller number of components and “units”, or may be divided into additional components and “units”

The term “current block” refers to one of a coding unit, a prediction unit, and a transform unit which are currently to be encoded or decoded. When, for convenience of description, there is a need to distinguish between blocks of other types such as a prediction unit, a transform unit, or the like, the terms “current coding block”, “current prediction block”, and “current transform block” may be used. In addition, the term “lower block” refers to a data unit split from the “current block”. The term “upper block” refers to a data unit including the “current block”.

Hereinafter, a “sample” refers to data that is allocated to a sampling location of an image and is a processing target. For example, pixel values in an image of a spatial domain or transform coefficients on a transformation domain may be samples. A unit including at least one sample may be defined as a block.

The present disclosure will now be described more fully with reference to the accompanying drawings for one of ordinary skill in the art to be able to perform the present disclosure without any difficulty. In addition, portions irrelevant to the descriptions of the present disclosure will be omitted in the drawings for clear descriptions of the present disclosure.

FIG. 1A illustrates a block diagram of an image encoding device 100 based on coding units according to a tree structure, according to an embodiment of the present disclosure.

The image encoding device 100 includes a largest coding unit determiner 110, a coding unit determiner 120, and an output unit 130.

The largest coding unit determiner 110 splits a picture or a slice included in the picture into a plurality of largest coding units, according to a size of a largest coding unit. The largest coding unit may be a data unit having a size of 32×32, 64×64, 128×128, 256×256, or the like, wherein a shape of the data unit is a square having a width and length in squares of 2. The largest coding unit determiner 110 may provide largest coding unit size information indicating the size of the largest coding unit to the output unit 130. The largest coding unit size information may be included in a bitstream by the output unit 130.

The coding unit determiner 120 determines coding units by splitting the largest coding unit. A coding unit may be determined by its largest size and depth. A depth may be defined as the number of times that the coding unit is spatially split from the largest coding unit. When the depth is increased by 1, the coding unit is split into at least two coding units. Therefore, when the depth is increased, sizes of coding units according to depths are each decreased. Whether to split a coding unit is determined according to whether splitting the coding unit is efficient according to rate-distortion optimization. Then, split information indicating whether the coding unit is to be split may be generated. The split information may be expressed in the form of a flag.

The coding unit may be split by using various methods. For example, a square coding unit may be split into four square coding units of which width and height are half of those of the square coding unit. The square coding unit may be split into two rectangular coding units of which width is half. The square coding unit may be split into two rectangular coding units of which height is half. The square coding unit may be split into three coding units in a manner that a width or height thereof is split by 1:2:1.

A rectangular coding unit of which width is twice as large as a height may be split into two square coding units. The rectangular coding unit of which width is twice as large as the height may be split into two rectangular coding units of which width is four times larger than a height. The rectangular coding unit of which width is twice as large as the height may be split into two rectangular coding units and one square coding unit in a manner that the width is split by 1:2:1.

Equally, a rectangular coding unit of which height is twice as large as a width may be split into two square coding units. The rectangular coding unit of which height is twice as large as the width may be split into two rectangular coding units of which height is four times larger than a width. Equally, the rectangular coding unit of which height is twice as large as the width may be split into two rectangular coding units and one square coding unit in a manner that the height is split by 1:2:1.

When the image encoding device 100 is capable of using two or more split methods, information about a split method that is usable to a coding unit, the split method being from among the split methods that are available to the image encoding device 100, may be determined for each picture. Therefore, only specific split methods may be used for each picture. When the image encoding device 100 uses only one split method, the information about a split method that is usable to a coding unit is not separately determined.

When split information of a coding unit indicates that the coding unit is to be split, split shape information indicating a split method with respect to the coding unit may be generated. When only one split method is usable in a picture including the coding unit, the split shape information may not be generated. When the split method is determined to be adaptive to encoding information adjacent to the coding unit, the split shape information may not be generated.

The largest coding unit may be split to smallest coding units according to smallest coding unit size information. A depth of the largest coding unit may be defined to be an uppermost depth, and a depth of the smallest coding units may be defined to be a lowermost depth. Therefore, a coding unit having an upper depth may include a plurality of coding units having a lower depth.

As described above, according to a largest size of a coding unit, image data of a current picture is split into a largest coding unit. The largest coding unit may include coding units that are split according to depths. Because the largest coding unit is split according to the depths, image data of a spatial domain included in the largest coding unit may be hierarchically split according to the depths.

A maximum depth that limits the maximum number of hierarchically splitting the largest coding unit or a minimum size of a coding unit may be preset.

The coding unit determiner 120 compares coding efficiency of hierarchically splitting a coding unit with coding efficiency of not splitting the coding unit. Then, the coding unit determiner 120 determines whether to split the coding unit according to a result of the comparison. When the coding unit determiner 120 determines that splitting the coding unit is more efficient, the coding unit determiner 120 hierarchically splits the coding unit. However, according to the result of the comparison, when the coding unit determiner 120 determines that not splitting the coding unit is more efficient, the coding unit determiner 120 does not split the coding unit. Whether to split the coding unit may be independently determined from whether a neighboring different coding unit is split.

According to an embodiment, whether to split the coding unit may be determined from a coding unit having a large depth, during an encoding procedure. For example, coding efficiency of a coding unit having a maximum depth is compared with coding efficiency of a coding unit having a depth that is less than the maximum depth by 1, and it is determined which one of coding units having the maximum depth and coding units having the depth that is less than the maximum depth by 1 is efficiently encoded in each area of a largest coding unit. According to a result of the determination, whether to split the coding units having the depth that is less than the maximum depth by 1 is determined in each area of the largest coding unit. Afterward, it is determined which one of coding units having a depth that is less than the maximum depth by 2 and one of the coding units having the maximum depth and the coding units having the depth that is less than the maximum depth by 1, the one having been selected according to the result of the determination, are further efficiently encoded in each area of the largest coding unit. The same determination process is performed on each of coding units having a smaller depth, and finally, whether to split the largest coding unit is determined according to which one of the largest coding unit and a hierarchical structure generated by hierarchically splitting the largest coding unit is further efficiently encoded.

Whether to split the coding unit may be determined from a coding unit having a small depth, during the encoding procedure. For example, coding efficiency of the largest coding unit is compared with coding efficiency of a coding unit of which depth is greater than the largest coding unit by 1, and it is determined which one of the largest coding unit and coding units of which depth is greater than the largest coding unit by 1 is efficiently encoded. When the coding efficiency of the largest coding unit is better, the largest coding unit is not split. When coding efficiency of the coding units of which depth is greater than the largest coding unit by 1 is better, the largest coding unit is split, and the comparison process is equally applied to split coding units.

When coding efficiency is examined from a coding unit having a large depth, calculation is large but a tree structure having high coding efficiency is obtained. On the contrary, when the coding efficiency is examined from a coding unit having a small depth, calculation is small but a tree structure having low coding efficiency is obtained. Therefore, in consideration of coding efficiency and calculation, an algorithm for obtaining a hierarchical tree structure of a largest coding unit may be designed by using various methods.

To determine efficiency of a coding unit according to each depth, the coding unit determiner 120 determines prediction and transformation methods that are most efficient to the coding unit. To determine the most efficient prediction and transformation methods, the coding unit may be split into predetermined data units. A data unit may have one of various shapes according to a method of splitting the coding unit. The method of splitting the coding unit which is performed to determine the data unit may be defined as a partition mode. For example, when a coding unit of 2N×2N (where N is a positive integer) is no longer split, a size of a prediction unit included in the coding unit is 2N×2N. When the coding unit of 2N×2N is split, the size of the prediction unit included in the coding unit may be 2N×N, N×2N, or N×N, according to the partition mode. The partition mode according to the present embodiment may generate symmetrical data units obtained by symmetrically splitting a height or width of the coding unit, data units obtained by asymmetrically splitting the height or width of the coding unit, such as 1:n or n:1, data units obtained by diagonally splitting the coding unit, data units obtained by geometrically splitting the coding unit, partitions having arbitrary shapes, or the like.

The coding unit may be predicted and transformed based on a data unit included in the coding unit. However, according to the present embodiment, a data unit for prediction and a data unit for transformation may be separately determined. The data unit for prediction may be defined as a prediction unit, and the data unit for transformation may be defined as a transform unit. A partition mode applied to the prediction unit and a partition mode applied to the transform unit may be different from each other, and prediction of the prediction unit and transformation of the transform unit may be performed in a parallel and independent manner in the coding unit.

To determine an efficient prediction method, the coding unit may be split into at least one prediction unit. Equally, to determine an efficient transformation method, the coding unit may be split into at least one transform unit. The split into the prediction unit and the split into the transform unit may be independently performed from each other. However, when a reconstructed sample in the coding unit is used in intra prediction, a dependent relation is established between prediction units or transform units included in the coding unit, so that the split into the prediction unit and the transform unit may affect each other.

The prediction unit included in the coding unit may be predicted through intra prediction or inter prediction. The intra prediction involves predicting prediction-unit samples by using reference samples adjacent to the prediction unit. The inter prediction involves predicting prediction-unit samples by obtaining reference samples from a reference picture that is referred to for a current picture.

For the intra prediction, the coding unit determiner 120 may apply a plurality of intra prediction methods to the prediction unit, thereby selecting the most efficient intra prediction method. The intra prediction method includes a discrete cosine (DC) mode, a planar mode, directional modes such as a vertical mode and a horizontal mode, or the like.

When a reconstructed sample adjacent to a coding unit is used as a reference sample, the intra prediction may be performed on each prediction unit. However, when a reconstructed sample in the coding unit is used as a reference sample, reconstruction with respect to the reference sample in the coding unit has to precede prediction with respect to the reference sample in the coding unit, so that a prediction order of a prediction unit may depend on a transformation order of a transform unit. Therefore, when the reconstructed sample in the coding unit is used as the reference sample, only an intra prediction method for transform units corresponding to the prediction unit, and actual intra prediction may be performed on each transform unit.

The coding unit determiner 120 may determine an optimal motion vector and a reference picture, thereby selecting the most efficient inter prediction method. For inter prediction, the coding unit determiner 120 may determine a plurality of motion vector candidates from a coding unit that is spatially and temporally adjacent to a current coding unit, and may determine, from among them, the most efficient motion vector to be a motion vector. Equally, the coding unit determiner 120 may determine a plurality of reference picture candidates from the coding unit that is spatially and temporally adjacent to the current coding unit, and may determine the most efficient reference picture from among them. According to an embodiment, the reference picture may be determined from reference picture lists that are predetermined with respect to a current picture. According to an embodiment, for accuracy of prediction, the most efficient motion vector from among the plurality of motion vector candidates may be determined to be a motion vector predictor, and a motion vector may be determined by compensating for the motion vector predictor. The inter prediction may be parallel performed on prediction units in the coding unit.

The coding unit determiner 120 may reconstruct the coding unit by obtaining only information indicating the motion vector and the reference picture, according to a skip mode. According to the skip mode, all encoding information including a residual signal is skipped, except for the information indicating the motion vector and the reference picture. Because the residual signal is skipped, the skip mode may be used when accuracy of prediction is very high.

A partition mode to be used may be limited according to the prediction method for the prediction unit. For example, only partition modes for a prediction unit having a size of 2N×2N or N×N may be applied to intra prediction, whereas partition modes for a prediction unit having a size of 2N×2N, 2N×N, N×2N, or N×N may be applied to inter prediction. In addition, only a partition mode for a prediction unit having a size of 2N×2N may be applied to a skip mode of the inter prediction. The image encoding device 100 may change a partition mode for each prediction method, according to coding efficiency.

The image encoding device 100 may perform transformation based on a coding unit or a transform unit included in the coding unit. The image encoding device 100 may transform residual data that is a difference value between an original value and a prediction value with respect to pixels included in the coding unit. For example, the image encoding device 100 may perform lossy-compression on the residual data through quantization and discrete cosine transform (DCT)/discrete sine transform (DST). Alternatively, the image encoding device 100 may perform lossless-compression on the residual data without the quantization.

The image encoding device 100 may determine a transform unit that is the most efficient one for quantization and transformation. The transform unit in the coding unit may be recursively split into smaller sized regions in a manner similar to that in which the coding unit is split according to the tree structure, according to an embodiment, such that residual data in the coding unit may be split according to the transform unit having the tree structure according to transformation depths. The image encoding device 100 may generate transformation split information about splitting the coding unit and the transform unit according to the determined tree structure of the transform unit.

A transformation depth indicating the number of splitting times to reach the transform unit by splitting the height and width of the coding unit may also be set in the image encoding device 100. For example, in a current coding unit of 2N×2N, a transformation depth may be 0 when the size of a transform unit is 2N×2N, may be 1 when the size of the transform unit is N×N, and may be 2 when the size of the transform unit is N/2×N/2. That is, the transform unit according to the tree structure may be set according to the transformation depth.

In conclusion, the coding unit determiner 120 determines a prediction method that is the most efficient one for a current prediction unit and is from among a plurality of intra prediction methods and inter prediction methods. Then, the coding unit determiner 120 determines a prediction unit determination scheme according to coding efficiency according to a prediction result. Equally, the coding unit determiner 120 determines a transform unit determination scheme according to coding efficiency according to a transformation result. According to the most efficient prediction unit and transform unit determination scheme, coding efficiency of a coding unit is finally determined. The coding unit determiner 120 finalizes a hierarchical structure of a largest coding unit, according to coding efficiency of a coding unit according to each depth.

The coding unit determiner 120 may measure coding efficiency of coding units according to depths, prediction efficiency of prediction methods, or the like by using Rate-Distortion Optimization based on Lagrangian multipliers.

The coding unit determiner 120 may generate split information indicating whether a coding unit is to be split according to each depth according to the determined hierarchical structure of the largest coding unit. Then, the coding unit determiner 120 may generate, for split coding units, partition mode information to be used in determining a prediction unit and transform unit split information to be used in determining a transform unit. In addition, when the coding unit may be split by using at least two split methods, the coding unit determiner 120 may generate both split information and split shape information that indicates a split method. The coding unit determiner 120 may generate information about the prediction method and the transformation method that are used in the prediction unit and the transform unit.

The output unit 130 may output, in a bitstream, a plurality of pieces of information generated by the largest coding unit determiner 110 and the coding unit determiner 120 according to the hierarchical structure of the largest coding unit.

A method of determining the coding unit, the prediction unit, and the transform unit according to the tree structure of the largest coding unit will be described below with reference to FIGS. 3 to 12 .

FIG. 1B illustrates a block diagram of an image decoding device 150 based on coding units according to a tree structure, according to an embodiment.

The image decoding device 150 includes a receiver 160, an encoding information extractor 170, and a decoder 180.

Definitions of the terms including a coding unit, a depth, a prediction unit, a transform unit, various split information, or the like for a decoding operation performed by the image decoding device 150 are equal to those described above with reference to FIG. 1A and the image encoding device 100. Because the image decoding device 150 is designed to reconstruct image data, various encoding methods used by the image encoding device 100 may also be applied to the image decoding device 150.

The receiver 160 receives and parses a bitstream with respect to an encoded video. The encoding information extractor 170 extracts, from the parsed bitstream, a plurality of pieces of information to be used in decoding largest coding units, and provides them to the decoder 180. The encoding information extractor 170 may extract information about a largest size of a coding unit of a current picture from a header, a sequence parameter set, or a picture parameter set of the current picture.

The encoding information extractor 170 extracts, from the parsed bitstream, a final depth and split information about coding units according to a tree structure according to each largest coding unit. The extracted final depth and split information are output to the decoder 180. The decoder 180 may split a largest coding unit according to the extracted final depth and split information, thereby determining a tree structure of the largest coding unit.

The split information extracted by the encoding information extractor 170 is split information about the tree structure determined to cause a minimum encoding error, the determination being performed by the image encoding device 100. Therefore, the image decoding device 150 may reconstruct an image by decoding data according to a decoding scheme that causes the minimum encoding error.

The encoding information extractor 170 may extract split information about a data unit such as a prediction unit and a transform unit included in the coding unit. For example, the encoding information extractor 170 may extract partition mode information about a partition mode that is the most efficient one for the prediction unit. The encoding information extractor 170 may extract transformation split information about a tree structure that is the most efficient one for the transform unit.

The encoding information extractor 170 may obtain information about the most efficient prediction method with respect to prediction units split from the coding unit. Then, the encoding information extractor 170 may obtain information about the most efficient transformation method with respect to transform units split from the coding unit.

The encoding information extractor 170 extracts the information from the bitstream, according to a method of configuring the bitstream, the method being performed by the output unit 130 of the image encoding device 100.

The decoder 180 may split a largest coding unit into coding units having the most efficient tree structure, based on the split information. Then, the decoder 180 may split the coding unit into the prediction units according to the partition mode information. The decoder 180 may split the coding unit into the transform units according to the transformation split information.

The decoder 180 may predict the prediction units according to the information about the prediction method. The decoder 180 may perform inverse quantization and inverse transformation on residual data that corresponds to a difference between an original value and a prediction value of a pixel, according to information about a method of transforming a transform unit. The decoder 180 may reconstruct pixels of the coding unit, according to a result of the prediction on the prediction units and a result of the transformation on the transform units.

FIG. 2 illustrates a process, performed by the image decoding device 150, of determining at least one coding unit by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine, by using block shape information, a shape of a coding unit, and may determine, by using split shape information, a shape according to which the coding unit is to be split. That is, a method of splitting a coding unit, which is indicated by the split shape information, may be determined based on which block shape is indicated by the block shape information used by the image decoding device 150.

According to an embodiment, the image decoding device 150 may use the block shape information indicating that a current coding unit has a square shape. For example, the image decoding device 150 may determine whether to split a square coding unit or not, whether to split the square coding unit vertically, whether to split the square coding unit horizontally, or whether to split the square coding unit into four coding units, according to the split shape information. Referring to FIG. 2 , when block shape information of a current coding unit 200 indicates a square shape, the decoder 180 may not split a coding unit 210 a having the same size as the current coding unit 200 according to split shape information indicating no split, or may determine coding units 210 b, 210 c, and 210 d split based on split shape information indicating a predetermined split method.

Referring to FIG. 2 , the image decoding device 150 may determine the two coding units 210 b obtained by splitting the current coding unit 200 in a vertical direction based on split shape information indicating split in a vertical direction, according to an embodiment. The image decoding device 150 may determine the two coding units 210 c obtained by splitting the current coding unit 200 in a horizontal direction based on split shape information indicating split in a horizontal direction. The image decoding device 150 may determine the four coding units 210 d obtained by splitting the current coding unit 200 in vertical and horizontal directions based on split shape information indicating split in vertical and horizontal directions. However, a split shape for splitting a square coding unit may not be limitedly interpreted to above shapes, and may include various shapes indicatable by split shape information. Predetermined split shapes for splitting a square coding unit will be described in detail below in various embodiments.

FIG. 3 illustrates a process, performed by the image decoding device 150, of determining at least one coding unit by splitting a coding unit having a non-square shape, according to an embodiment.

According to an embodiment, the image decoding device 150 may use block shape information indicating that a current coding unit has a non-square shape. The image decoding device 150 may determine whether or not to split the current coding unit having the non-square shape, or whether to split the current coding unit having the non-square shape by using a predetermined method. Referring to FIG. 3 , when block shape information of a current coding unit 300 or 350 indicates a non-square shape, the image decoding device 150 may not split a coding unit 310 or 360 having the same size as the current coding unit 300 or 350 according to split shape information indicating no split, or may determine coding units 320 a, 320 b, 330 a, 330 b, 330 c, 370 a, 370 b, 380 a, 380 b, and 380 c split according to split shape information indicating a predetermined split method. A predetermined split method of splitting a non-square coding unit will be described in detail below in various embodiments.

According to an embodiment, the image decoding device 150 may determine, by using the split shape information, a shape of a coding unit is split, and in this case, the split shape information may indicate the number of at least one coding unit generated when a coding unit is split. Referring to FIG. 3 , when the split shape information indicates that the current coding unit 300 or 350 is to be split into two coding units, the image decoding device 150 may determine the two coding units 320 a and 320 b or 370 a and 370 b, which are respectively included in the current coding unit 300 or 350 by splitting the current coding unit 300 or 350 based on the split shape information.

According to an embodiment, when the image decoding device 150 splits the current coding unit 300 or 350 having the non-square shape based on the split shape information, the image decoding device 150 may split the current coding unit 300 or 350 having the non-square shape in consideration of a location of a longer side. For example, the image decoding device 150 may determine a plurality of coding units by splitting the current coding unit 300 or 350 in a direction of splitting the longer sides of the current coding unit 300 or 350 in consideration of the shape of the current coding unit 300 or 350.

According to an embodiment, when split shape information indicates that a coding unit is to be split into an odd number of blocks, the image decoding device 150 may determine an odd number of coding units included in the current coding unit 300 or 350. For example, when split shape information indicates that the current coding unit 300 or 350 is to be split into three coding units, the image decoding device 150 may split the current coding unit 300 or 350 into the three coding units 330 a, 330 b, and 330 c or 380 a, 380 b, and 380 c. According to an embodiment, the image decoding device 150 may determine the odd number of coding units included in the current coding unit 300 or 350, wherein sizes of the determined coding units may not be equal. For example, a size of the coding unit 330 b or 380 b from among the odd number of coding units 330 a, 330 b, and 330 c or 380 a, 380 b, and 380 c may be different from sizes of the coding units 330 a and 330 c or 380 a or 380 c. That is, coding units that may be determined when the current coding unit 300 or 350 is split may have different types of a size.

According to an embodiment, when split shape information indicates that a coding unit is to be split into an odd number of blocks, the image decoding device 150 may determine an odd number of coding units included in the current coding unit 300 or 350 and may set a predetermined limit on at least one coding unit from among the odd number of coding units generated by splitting the current coding unit 300 or 350. Referring to FIG. 3 , the image decoding device 150 may decode the coding unit 330 b or 380 b at the center of the three coding units 330 a, 330 b, and 330 c or 380 a, 380 b, and 380 c generated when the current coding unit 300 or 350 is split in a different manner from the coding units 330 a and 330 c or 380 a and 380 c. For example, the image decoding device 150 may limit the coding unit 330 b or 380 b at the center not to be further split unlike the coding units 330 a and 330 c or 380 a and 380 c, or to be split only a certain number of times.

FIG. 4 illustrates a process of splitting, by the image decoding device 150, a coding unit based on at least one of block shape information and split shape information, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine whether to split a first coding unit 400 having a square shape into coding units based on at least one of block shape information and split shape information. According to an embodiment, when the split shape information indicates a split of the first coding unit 400 in a horizontal direction, the image decoding device 150 may determine a second coding unit 410 by splitting the first coding unit 400 in the horizontal direction. The terms “first coding unit”, “second coding unit”, and “third coding unit” according to an embodiment are used in the context of splitting a coding unit. For example, a second coding unit may be determined when a first coding unit is split, and a third coding unit may be determined when the second coding unit is split. Relations between the first through third coding units used hereinafter may be understood to follow the above order characteristics.

According to an embodiment, the image decoding device 150 may determine whether to split the determined second coding unit 410 into coding units based on at least one of block shape information and split shape information. Referring to FIG. 4 , the image decoding device 150 may split the second coding unit 410, which has a non-square shape determined by splitting the first coding unit 400, into at least one third coding unit, for example, third coding units 420 a, 420 b, 420 c, and 420 d, based on at least one of block shape information and split shape information, or may not split the second coding unit 410. The image decoding device 150 may obtain at least one of block shape information and split shape information, the image decoding device 150 may split the first coding unit 400 based on at least one of the block shape information and the split shape information to obtain a plurality of second coding units (for example, the second coding unit 410) having various shapes, and the second coding unit 410 may be split according to a manner of splitting the first coding unit 400 based on at least one of the block shape information and the split shape information. According to an embodiment, when the first coding unit 400 is split into the second coding units 410 based on at least one of block shape information and split shape information about the first coding unit 400, the second coding unit 410 may also be split into the third coding units, for example, the third coding units 420 a, 420 b, and 420 c, 420 d, based on at least one of block shape information and split shape information about the second coding unit 410. That is, a coding unit may be recursively split based on at least one of split shape information and block shape information related to the coding unit. A method used to recursively split a coding unit will be described below in various embodiments.

According to an embodiment, the image decoding device 150 may determine to split each of the third coding units (for example, the third coding units 420 a, 420 b, 420 c, and 420 d) into coding units or not to split the second coding unit 410 based on at least one of block shape information and split shape information. The image decoding device 150 may split the second coding unit 410 having a non-square shape into the odd number of third coding units 420 b, 420 c, and 420 d. The image decoding device 150 may set a predetermined limitation on a predetermined third coding unit from among the odd number of third coding units 420 b, 420 c, and 420 d. For example, the image decoding device 150 may limit the coding unit 420 c located at the center from among the odd number of third coding units 420 b, 420 c, and 420 d to be split no more or to be split to a settable number of times. Referring to FIG. 4 , the image decoding device 150 may limit the coding unit 420 c located at the center from among the odd number of third coding units 420 b, 420 c, and 420 d included in the second coding unit 410 having a non-square shape to be split no more, to be split into a predetermined split manner (for example, split only into four coding units or split into a shape corresponding to that into which the second coding unit 410 is split), or to be split only a predetermined number of times (for example, split only n times, wherein n>0). However, the limitations on the coding unit 420 c located at the center are simply embodiments, and thus the present disclosure should not be construed as being limited to the above embodiments, and it should be interpreted that the limitations include various limitations of decoding the coding unit 420 c located at the center differently from the coding units 420 b and 420 d.

According to an embodiment, the image decoding device 150 may obtain, from a predetermined location in a current coding unit, at least one of block shape information and split shape information used to split the current coding unit.

According to an embodiment, when the current coding unit is split into a predetermined number of coding units, the image decoding device 150 may select one of the coding units. A method of selecting one of a plurality of coding units may vary, and descriptions about such a method will be described below in various embodiments.

According to an embodiment, the image decoding device 150 may split the current coding unit into the plurality of coding units, and may determine the coding unit at the predetermined location.

FIG. 5 illustrates a method of determining, by the image decoding device 150, a coding unit at a predetermined location from among an odd number of coding units, according to an embodiment.

According to an embodiment, the image decoding device 150 may use information indicating a location of each of an odd number of coding units so as to determine a coding unit located at the center of the odd number of coding units. Referring to FIG. 5 , the image decoding device 150 may determine an odd number of coding units 520 a, 520 b, and 520 c by splitting a current coding unit 500. The image decoding device 150 may determine the coding unit 520 b at the center by using information about locations of the odd number of coding units 520 a, 520 b, and 520 c. For example, the image decoding device 150 may determine the coding unit 520 located at the center by determining locations of the coding units 520 a, 520 b, and 520 c based on information indicating locations of predetermined samples included in the coding units 520 a, 520 b, and 520 c. In detail, the image decoding device 150 may determine the coding unit 520 b located at the center by determining the locations of the coding units 520 a, 520 b, and 520 c based on information indicating locations of upper-left samples 530 a, 530 b, and 530 c of the coding units 520 a, 520 b, and 520 c.

According to an embodiment, the information indicating the locations of the upper-left samples 530 a, 530 b, and 530 c respectively included in the coding units 520 a, 520 b, and 520 c may include information about locations or coordinates in a picture of the coding units 520 a, 520 b, and 520 c. According to an embodiment, the information indicating the locations of the upper-left samples 530 a, 530 b, and 530 c respectively included in the coding units 520 a, 520 b, and 520 c may include information indicating widths or heights of the coding units 520 a, 520 b, and 520 c included in the current coding unit 500, wherein the widths or heights may correspond to information indicating differences between coordinates in the picture of the coding units 520 a, 520 b, and 520 c. That is, the image decoding device 150 may determine the coding unit 520 b located at the center by directly using the information about the locations or coordinates in the picture of the coding units 520 a, 520 b, and 520 c, or by using the information about the widths or heights of the coding units, which indicate difference values between coordinates.

According to an embodiment, the information indicating the location of the upper-left sample 530 a of the top coding unit 520 a may indicate (xa, ya) coordinates, information indicating the location of the upper-left sample 530 b of the center coding unit 520 b may indicate (xb, yb) coordinates, and the information indicating the location of the upper-left sample 530 c of the bottom coding unit 520 c may indicate (xc, yc) coordinates. The image decoding device 150 may determine the center coding unit 520 b by using the coordinates of the upper-left samples 530 a, 530 b, and 530 c respectively included in the coding units 520 a, 520 b, and 520 c. For example, when the coordinates of the upper-left samples 530 a, 530 b, and 530 c are aligned in an ascending order or descending order, the center coding unit 520 b including (xb, yb) that is coordinates of the upper-left sample 530 b may be determined as a coding unit located at the center from among the coding units 520 a, 520 b, and 520 c determined when the current coding unit 500 is split. Here, the coordinates indicating the locations of the upper-left samples 530 a, 530 b, and 530 c may indicate coordinates indicating absolute locations in the picture, and further, may use (dxb, dyb) coordinates that are information indicating a relative location of the upper-left sample 530 b of the center coding unit 520 b and (dxc, dyc) coordinates that are information indicating a relative location of the upper-left sample 530 c of the bottom coding unit 520 c, based on the location of the upper-left sample 530 c of the top coding unit 520 a. Also, a method of determining a coding unit at a predetermined location by using coordinates of a sample included in a coding unit as information indicating a location of the sample should not be limitedly interpreted to the above method, and may be interpreted to various arithmetic methods capable of using coordinates of a sample.

According to an embodiment, the image decoding device 150 may split the current coding unit 500 into the plurality of coding units 520 a, 520 b, and 520 c, and select a coding unit from among the coding units 520 a, 520 b, and 520 c according to a predetermined criterion. For example, the image decoding device 150 may select the coding unit 520 b that has a different size from among the coding units 520 a, 520 b, and 520 c.

According to an embodiment, the image decoding device 150 may determine the width or height of each of the coding units 520 a, 520 b, and 520 c by using the (xa, ya) coordinates that are the information indicating the location of the upper-left sample 530 a of the top coding unit 520 a, the (xb, yb) coordinates that are the information indicating the location of the upper-left sample 530 b of the center coding unit 520 b, and the (xc, yc) coordinates that are the information indicating the location of the upper-left sample 530 c of the bottom coding unit 520 c. The image decoding device 150 may determine a size of each of the coding units 520 a, 520 b, and 520 c by using the coordinates (xa, ya), (xb, yb), and (xc, yc) indicating the locations of the coding units 520 a, 520 b, and 520 c.

According to an embodiment, the image decoding device 150 may determine the width of the top coding unit 520 a to xb-xa and the height to yb-ya. According to an embodiment, the image decoding device 150 may determine the width of the center coding unit 520 b to xc-xb and the height to yc-yb. According to an embodiment, the image decoding device 150 may determine the width or height of the bottom coding unit by using the width or height of the current coding unit, and the width and height of the top coding unit 520 a and the center coding unit 520 b. The image decoding device 150 may determine one coding unit having a size different from other coding units based on the determined widths and heights of the coding units 520 a, 520 b, and 520 c. Referring to FIG. 5 , the image decoding device 150 may determine, as the coding unit at the predetermined location, the center coding unit 520 b having a size different from sizes of the top coding unit 520 a and the bottom coding unit 520 c. However, because a process of determining, by the image decoding device 150, a coding unit having a size different from other coding units is only an embodiment of determining a coding unit at a predetermined location by using sizes of coding units determined based on sample coordinates, various processes of determining a coding unit at a predetermined location by comparing sizes of coding units determined according to predetermined sample coordinates may be used.

However, a location of a sample which is considered to determine a location of a coding unit should not be construed as being limited to the upper-left, but may be interpreted that information about a location of an arbitrary sample included in a coding unit is usable.

According to an embodiment, the image decoding device 150 may select a coding unit at a predetermined location from among an odd number of coding units that are determined when a current coding unit is split, in consideration of a shape of the current coding unit. For example, when the current coding unit has a non-square shape in which a width is longer than a height, the image decoding device 150 may determine the coding unit at the predetermined location along a horizontal direction. In other words, the image decoding device 150 may determine a coding unit from among coding units having different locations in the horizontal direction, and may set a limitation on the coding unit. When the current coding unit has the non-square shape in which the height is longer than the width, the image decoding device 150 may determine the coding unit at the predetermined location along a vertical direction. In other words, the image decoding device 150 may determine a coding unit from among coding units having different locations in the vertical direction, and set a limitation on the coding unit.

According to an embodiment, the image decoding device 150 may use information indicating a location of each of an even number of coding units so as to determine a coding unit at a predetermined location from among the even number of coding units. The image decoding device 150 may determine the even number of coding units by splitting a current coding unit, and determine the coding unit at the predetermined location by using the information about the locations of the even number of coding units. Detailed processes thereof may correspond to processes of determining a coding unit at a predetermined location (for example, a center location) from among an odd number of coding units, which have been described above with reference to FIG. 5 , and thus descriptions thereof are not provided again.

According to an embodiment, when a current coding unit having a non-square shape is split into a plurality of coding units, predetermined information about a coding unit at a predetermined location may be used during a split process so as to determine the coding unit at the predetermined location from among the plurality of coding units. For example, the image decoding device 150 may use at least one of block shape information and split shape information, which are stored in a sample included in a center coding unit during a split process so as to determine a coding unit located at the center from among a plurality of coding units obtained by splitting a current coding unit.

Referring to FIG. 5 , the image decoding device 150 may split the current coding unit 500 into the plurality of coding units 520 a, 520 b, and 520 c based on at least one of block shape information and split shape information, and determine the coding unit 520 b located at the center from among the plurality of coding units 520 a, 520 b, and 520 c. In addition, the image decoding device 150 may determine the coding unit 520 b located at the center in consideration of a location where at least one of the block shape information and the split shape information is obtained. That is, at least one of the block shape information and the split shape information of the current coding unit 500 may be obtained from the sample 540 located at the center of the current coding unit 500, and when the current coding unit 500 is split into the plurality of coding units 520 a, 520 b, and 520 c based on at least one of the block shape information and the split shape information, the coding unit 520 b including the sample 540 may be determined as the coding unit located at the center. However, information used to determine a coding unit located at the center should not be construed as being limited to at least one of block shape information and split shape information, and various types of information may be used during a process of determining a coding unit located at the center.

According to an embodiment, predetermined information for identifying a coding unit at a predetermined location may be obtained from a predetermined sample included in a coding unit to be determined. Referring to FIG. 5 , the image decoding device 150 may use at least one of block shape information and split shape information obtained from a sample located at a predetermined location in the current coding unit 500 (for example, a sample located at the center of the current coding unit 500) so as to determine a coding unit at a predetermined location from among the plurality of coding units 520 a, 520 b, and 520 c determined when the current coding unit 500 is split (for example, a coding unit located at the center from among the plurality of coding units). That is, the image decoding device 150 may determine the sample at the predetermined location by referring to a block shape of the current coding unit 500, and the image decoding device 150 may determine and set a predetermined limitation on the coding unit 520 b including the sample from which predetermined location (for example, at least one of the block shape information and the split shape information) is obtained, from among the plurality of coding units 520 a, 520 b, and 520 c determined when the current coding unit 500 is split. Referring to FIG. 5 , the image decoding device 150 may determine the sample 540 located at the center of the current coding unit 500, as the sample from which the predetermined information is obtained, and the image decoding device 150 may set the predetermined location during a decoding process, on the coding unit 520 b including the sample 540. However, a location of a sample from which predetermined information is obtained should not be construed as being limited to the above location, and the sample may be interpreted to samples at arbitrary locations included in the coding unit 520 determined to be limited.

According to an embodiment, a location of a sample from which predetermined location is obtained may be determined based on a shape of the current coding unit 500. According to an embodiment, block shape information may be used to determine whether a shape of a current coding unit is a square or a non-square, and a location of a sample from which predetermined information is obtained may be determined based on the shape. For example, the image decoding device 150 may determine, as a sample from which predetermined information is obtained, a sample located on a boundary of splitting at least one of a width and a height of a current coding unit into halves by using at least one of information about the width of the current coding unit and information about the height of the current coding unit. As another example, when block shape information about a current coding unit indicates a non-square shape, the image decoding device 150 may determine, as a sample from which predetermined information is obtained, one of samples adjacent to a boundary of splitting a longer side of the current coding unit into halves.

According to an embodiment, when a current coding unit is split into a plurality of coding units, the image decoding device 150 may use at least one of block shape information and split shape information so as to determine a coding unit at a predetermined location from among the plurality of coding units. According to an embodiment, the image decoding device 150 may obtain at least one of the block shape information and the split shape information from a sample at a predetermined location included in the coding unit, and the image decoding device 150 may split the plurality of coding units generated when the current coding unit is split by using at least one of the split shape information and the block shape information obtained from the sample at the predetermined location included in each of the plurality of coding units. In other words, the coding unit may be recursively split by using at least one of the block shape information and the split shape information obtained from the sample at the predetermined location in each coding unit. Because a process of recursively splitting a coding unit has been described above with reference to FIG. 4 , details thereof are not provided again.

According to an embodiment, the image decoding device 150 may determine at least one coding unit by splitting a current coding unit, and may determine an order of decoding the at least one coding unit according to a predetermined block (for example, a current coding unit).

FIG. 6 illustrates an order of processing a plurality of coding units when the image decoding device 150 determines the plurality of coding units by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine, according to block shape information and split shape information, second coding units 610 a and 610 b by splitting a first coding unit 600 in a vertical direction, second coding units 630 a and 630 b by splitting the first coding unit 600 in a horizontal direction, or second coding units 650 a, 650 b, 650 c, and 650 d by splitting the first coding unit 600 in vertical and horizontal directions.

Referring to FIG. 6 , the image decoding device 150 may determine an order such that the second coding units 610 a and 610 b determined by splitting the first coding unit 600 in the vertical direction to be processed in a horizontal direction 610 c. The image decoding device 150 may determine a processing order of the second coding units 630 a and 630 b determined by splitting the first coding unit 600 in the horizontal direction to be in a vertical direction 630 c. The image decoding device 150 may determine the second coding units 650 a, 650 b, 650 c, and 650 d determined by splitting the first coding unit 600 in the vertical and horizontal directions to be processed according to a predetermined order (for example, a raster scan order or a z-scan order 650 e) in which coding units in one row are processed and then coding units in a next row are processed.

According to an embodiment, the image decoding device 150 may recursively split coding units. Referring to FIG. 6 , the image decoding device 150 may determine a plurality of coding units 610 a, 610 b, 630 a, 630 b, 650 a, 650 b, 650 c, and 650 d by splitting the first coding unit 600, and may recursively split each of the determined plurality of coding units 610 a, 610 b, 630 a, 630 b, 650 a, 650 b, 650 c, and 650 d. A method of splitting the plurality of coding units 610 a, 610 b, 630 a, 630 b, 650 a, 650 b, 650 c, and 650 d may be similar to a method of splitting the first coding unit 600. Accordingly, the plurality of coding units 610 a, 610 b, 630 a, 630 b, 650 a, 650 b, 650 c, and 650 d may each be independently split into a plurality of coding units. Referring to FIG. 6 , the image decoding device 150 may determine the second coding units 610 a and 610 b by splitting the first coding unit 600 in the vertical direction, and in addition, may determine to split or not to split each of the second coding units 610 a and 610 b independently.

According to an embodiment, the image decoding device 150 may split the left second coding unit 610 a in the horizontal direction to obtain third coding units 620 a and 620 b, and may not split the right second coding unit 610 b.

According to an embodiment, a processing order of coding units may be determined based on a process of splitting coding units. In other words, a processing order of split coding units may be determined based on a processing order of coding units just before being split. The image decoding device 150 may determine an order of processing the third coding units 620 a and 620 b determined when the left second coding unit 610 a is split independently from the right second coding unit 610 b. Because the third coding units 620 a and 620 b are determined when the left second coding unit 610 a is split in the horizontal direction, the third coding units 620 a and 620 b may be processed in a vertical direction 620 c. Also, because the order of processing the left second coding unit 610 a and the right second coding unit 610 b is in the horizontal direction 610 c, the third coding units 620 a and 620 b included in the left second coding unit 610 a may be processed in the vertical direction 620 c and then the right second coding unit 610 b may be processed. Because the above descriptions are for describing a process of determining a processing order according to coding units before being split, the process should not be limitedly interpreted to the above embodiments, and various methods of independently processing coding units split and determined in various shapes according to a predetermined order may be used.

FIG. 7 illustrates a process of determining, by the image decoding device 150, a current coding unit to be split into an odd number of coding units when coding units are unable to be processed in a predetermined order, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine that the current coding unit is split into the odd number of coding units based on obtained block shape information and split shape information. Referring to FIG. 7 , a first coding unit 700 having a square shape may be split into second coding units 710 a and 710 b having non-square shapes, and the second coding units 710 a and 710 b may be independently split into third coding units 720 a, 720 b, 720 c, 720 d, and 720 e. According to an embodiment, the image decoding device 150 may determine a plurality of the third coding units 720 a and 720 b by splitting the left coding unit 710 a from among the second coding units in a horizontal direction, and the right coding unit 710 b may be split into an odd number of the third coding units 720 c, 720 d, and 720 e.

According to an embodiment, the image decoding device 150 may determine whether a coding unit split into an odd number exists by determining whether the third coding units 720 a, 720 b, 720 c, 720 d, and 720 e are processable in a predetermined order. Referring to FIG. 7 , the image decoding device 150 may determine the third coding units 720 a, 720 b, 720 c, 720 d, and 720 e by recursively splitting the first coding unit 700. The image decoding device 150 may determine, based on at least one of block shape information and split shape information, whether there is a coding unit split into an odd number from among the first coding unit 700, the second coding units 710 a and 710 b, and the third coding units 720 a, 720 b, 720 c, 720 d, and 720 e. For example, a coding unit located at the right from among the second coding units 710 a and 710 b may be split into the odd number of third coding units 720 c, 720 d, and 720 e. An order of processing a plurality of coding units included in the first coding unit 700 may be a predetermined order 730 (for example, a z-scan order), and the image decoding device 150 may determine whether the third coding units 720 c, 720 d, and 720 e determined when the right second coding unit 710 b is split into an odd number satisfy a condition of being processable according to the predetermined order.

According to an embodiment, the image decoding device 150 may determine whether the third coding units 720 a, 720 b, 720 c, 720 d, and 720 e included in the first coding unit 700 satisfy a condition of being processable according to a predetermined order, wherein the condition is related to whether at least one of a width and a height of the second coding units 710 a and 710 b is split into halves along boundaries of the third coding units 720 a, 720 b, 720 c, 720 d, and 720 e. For example, the third coding units 720 a and 720 b that are determined when the left second coding unit 710 a having a non-square shape is split into halves satisfy the condition, but the third coding units 720 c, 720 d, and 720 e do not satisfy the condition because the boundaries of the third coding units 720 c, 720 d, and 720 e that are determined when the right second coding unit 710 b is split into three coding units are unable to split a width or height of the right second coding unit 710 b into halves. Also, the image decoding device 150 may determine disconnection of a scan order when the condition is dissatisfied, and determine that the right second coding unit 710 b is split into an odd number of coding units based on the determination result. According to an embodiment, when a coding unit is split into an odd number of coding units, the image decoding device 150 may set a predetermined limitation on a coding unit at a predetermined location from among the coding units, and because details about the limitation or the predetermined location have been described above in various embodiments, details thereof are not provided again.

FIG. 8 illustrates a process of determining, by the image decoding device 150, at least one coding unit when a first coding unit 800 is split, according to an embodiment. According to an embodiment, the image decoding device 150 may split the first coding unit 800 based on at least one of block shape information and split shape information obtained through the receiver 160. The first coding unit 800 having a square shape may be split into four coding units having square shapes or non-square shapes. For example, referring to FIG. 8 , when block shape information indicates that the first coding unit 800 is a square and split shape information indicates that the first coding unit 800 is to be split into non-square coding units, the image decoding device 150 may split the first coding unit 800 into a plurality of non-square coding units. In detail, when the split shape information indicates that the first coding unit 800 is to be split into a horizontal or vertical direction to determine an odd number of coding units, the image decoding device 150 may split the first coding unit 800 having a square shape into, as the odd number of coding units, second coding units 810 a, 810 b, and 810 c determined when the first coding unit 800 is split in the vertical direction, or second coding units 820 a, 820 b, and 820 c determined when the first coding unit 800 is split in the horizontal direction.

According to an embodiment, the image decoding device 150 may determine whether the second coding units 810 a, 810 b, and 810 c and 820 a, 820 b, and 820 c included in the first coding unit 800 satisfy a condition of being processable according to a predetermined order, wherein the condition is related to whether at least one of the width and the height of the first coding unit 800 is split into halves along the boundaries of the second coding units 810 a, 810 b, and 810 c and 820 a, 820 b, and 820 c. Referring to FIG. 8 , because the boundaries of the second coding units 810 a, 810 b, and 810 c determined when the first coding unit 800 having a square shape is split in the vertical direction are unable to split the width of the first coding unit 800 into halves, it may be determined that the first coding unit 800 does not satisfy the condition of being processable according to the predetermined order. Also, because the boundaries of the second coding units 820 a, 820 b, and 820 c determined when the first coding unit 800 having a square shape is split in the horizontal direction are unable to split the width of the first coding unit 800 into halves, it may be determined that the first coding unit 800 does not satisfy the condition of being processable according to the predetermined order. When the condition is dissatisfied, the image decoding device 150 determines disconnection of a scan order and may determine that the first coding unit 800 is split into an odd number of coding units based on the determination result. According to an embodiment, when a coding unit is split into an odd number of coding units, the image decoding device 150 may set a predetermined limitation on a coding unit at a predetermined location from among the coding units, and because details about the limitation or the predetermined location have been described above in various embodiments, details thereof are not provided again.

According to an embodiment, the image decoding device 150 may determine coding units having various shapes by splitting a first coding unit.

Referring to FIG. 8 , the image decoding device 150 may split the first coding unit 800 having a square shape and a first coding unit 830 or 850 having a non-square shape into coding units having various shapes.

FIG. 9 illustrates that, when a second coding unit having a non-square shape, which is determined when a first coding unit 900 is split, satisfies a predetermined condition, a shape of the second coding unit that is splittable is limited by the image decoding device 150, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine, based on at least one of block shape information and split shape information obtained through the receiver 160, to split the first coding unit 900 having a square shape into second coding units 910 a, 910 b, 920 a, and 920 b having non-square shapes. The second coding units 910 a, 910 b, 920 a, and 920 b may be independently split. Accordingly, the image decoding device 150 may determine to split or not to split the second coding units 910 a, 910 b, 920 a, and 920 b based on at least one of block shape information and split shape information related to each of the second coding units 910 a, 910 b, 920 a, and 920 b. According to an embodiment, the image decoding device 150 may determine third coding units 912 a and 912 b by splitting the left second coding unit 910 a having a non-square shape and determined when the first coding unit 900 is split in a vertical direction. However, when the left second coding unit 910 a is split in a horizontal direction, the image decoding device 150 may limit the right second coding unit 910 b not to be split in the horizontal direction like a direction in which the left second coding unit 910 a is split. When the right second coding unit 910 b is split in the same direction and third coding units 914 a and 914 b are determined, the third coding units 912 a, 912 b, 914 a, and 914 b may be determined when the left second coding unit 910 a and the right second coding unit 910 b are independently split in the horizontal direction. However, this is the same result as the image decoding device 150 splitting the first coding unit 900 into four second coding units 930 a, 930 b, 930 c, and 930 d having square shapes based on at least one of block shape information and split shape information, and thus may be inefficient in terms of image decoding.

According to an embodiment, the image decoding device 150 may determine third coding units 922 a, 922 b, 924 a, and 924 b by splitting the second coding units 920 a or 920 b having a non-square shape and determined when the first coding unit 900 is split in the horizontal direction. However, when one of second coding units (for example, the top second coding unit 920 a) is split in the vertical direction, the image decoding device 150 may limit the other second coding unit (for example, the bottom second coding unit 920 b) not to be split in the vertical direction like a direction in which the top second coding unit 920 a is split based on the above reasons.

FIG. 10 illustrates a process of splitting, by the image decoding device 150, a coding unit having a square shape when split shape information indicates that the coding unit is not to be split into four coding units having square shapes, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine second coding units 1010 a, 1010 b, 1020 a, 1020 b, and the like by splitting a first coding unit 1000 based on at least one of block shape information and split shape information. The split shape information may include information about various shapes into which a coding unit is splittable, but sometimes, the information about various shapes may not include information for splitting a coding unit into four square coding units. According to such split shape information, the image decoding device 150 is unable to split the first coding unit 1000 having a square shape into four square second coding units 1030 a, 1030 b, 1030 c, and 1030 d. Based on the split shape information, the image decoding device 150 may determine the second coding units 1010 a, 1010 b, 1020 a, 1020 b, and the like having non-square shapes.

According to an embodiment, the image decoding device 150 may independently split the second coding units 1010 a, 1010 b, 1020 a, 1020 b, and the like having non-square shapes. Each of the second coding units 1010 a, 1010 b, 1020 a, 1020 b, and the like may be split in a predetermined order through a recursive method that may correspond to a method of splitting the first coding unit 1000 based on at least one of block shape information and split shape information.

For example, the image decoding device 150 may determine third coding units 1012 a and 1012 b having square shapes by splitting the left second coding unit 1010 a in a horizontal direction and may determine third coding units 1014 a and 1014 b having square shapes by splitting the right second coding unit 1010 b in a horizontal direction. In addition, the image decoding device 150 may determine third coding units 1016 a, 1016 b, 1016 c, and 1016 d having square shapes by splitting both the left second coding unit 1010 a and the right second coding unit 1010 b in the horizontal direction. In this case, coding units may be determined in the same manner in which the first coding unit 1000 is split into the four square second coding units 1030 a, 1030 b, 1030 c, and 1030 d.

As another example, the image decoding device 150 may determine third coding units 1022 a and 1022 b having square shapes by splitting the top second coding unit 1020 a in the vertical direction and determine third coding units 1024 a and 1024 b having square shapes by splitting the bottom second coding unit 1020 b in the vertical direction. In addition, the image decoding device 150 may determine third coding units 1022 a, 1022 b, 1024 a, and 1024 b having square shapes by splitting both the top second coding unit 1020 a and the bottom second coding unit 1020 b in the vertical direction. In this case, coding units may be determined in the same manner in which the first coding unit 1000 is split into the four square second coding units 1030 a, 1030 b, 1030 c, and 1030 d.

FIG. 11 illustrates that a processing order between a plurality of coding units may be changed according to a process of splitting a coding unit, according to an embodiment.

According to an embodiment, the image decoding device 150 may split a first coding unit 1100, based on block shape information and split shape information. When the block shape information indicates a square shape and the split shape information indicates that the first coding unit 1100 is to be split in at least one of a horizontal direction and a vertical direction, the image decoding device 150 may split the first coding unit 1100 to determine second coding units (for example, second coding units 1110 a, 1110 b, 1120 a, 1120 b, 1130 a, 1130 b, 1130 c, 1130 d, and the like). Referring to FIG. 11 , the second coding units 1110 a, 1110 b, 1120 a, and 1120 b having non-square shapes and determined when the first coding unit 1100 is split only in the horizontal or vertical direction may each be independently split based on block shape information and split shape information about each of the second coding units 1110 a, 1110 b, 1120 a, and 1120 b. For example, the image decoding device 150 may determine third coding units 1116 a, 1116 b, 1116 c, and 1116 d by splitting the second coding units 1110 a and 1110 b in the horizontal direction, wherein the second coding units 1110 a and 1110 b are generated when the first coding unit 1100 is split in the vertical direction, and may determine third coding units 1126 a, 1126 b, 1126 c, and 1126 d by splitting the second coding units 1120 a and 1120 b in the horizontal direction, wherein the second coding units 1120 a and 1120 b are generated when the first coding unit 1100 is split in the horizontal direction. Because split processes of the second coding units 1110 a, 1110 b, 1120 a, and 1120 b have been described with reference to FIG. 9 , details thereof are not provided again.

According to an embodiment, the image decoding device 150 may process coding units according to a predetermined order. Because characteristics about processing of coding units according to a predetermined order have been described above with reference to FIG. 6 , details thereof are not provided again. Referring to FIG. 11 , the image decoding device 150 may determine four square third coding units 1116 a, 1116 b, 1116 c, and 1116 d or 1126 a, 1126 b, 1126 c, and 1126 d by splitting the first coding unit 1100 having a square shape. According to an embodiment, the image decoding device 150 may determine a processing order of the third coding units 1116 a, 1116 b, 1116 c, and 1116 d or 1126 a, 1126 b, 1126 c, and 1126 d according to a shape of the first coding unit 1100 being split.

According to an embodiment, the image decoding device 150 may determine the third coding units 1116 a, 1116 b, 1116 c, and 1116 d by splitting each of the second coding units 1110 a and 1110 b in the horizontal direction, wherein the second coding units 1110 a and 1110 b are generated when the first coding unit 1100 is split in the vertical direction, and the image decoding device 150 may process the third coding units 1116 a, 1116 b, 1116 c, and 1116 d according to an order 1117 of first processing the third coding units 1116 a and 1116 b included in the left second coding unit 1110 a in the vertical direction and then processing the third coding units 1116 c and 1116 d included in the right second coding unit 1110 b in the vertical direction.

According to an embodiment, the image decoding device 150 may determine the second coding units 1126 a, 1126 b, 1126 c, and 1126 d by splitting each of the second coding units 1120 a and 1120 b in the vertical direction, wherein the second coding units1120 a and 1120 b are generated when the first coding unit 1100 is split in the horizontal direction, and the image decoding device 150 may process the third coding units 1126 a, 1126 b, 1126 c, and 1126 d according to an order of first processing the third coding units 1126 a and 1126 b included in the top second coding unit 1120 a in the horizontal direction and then processing the third coding units 1126 c and 1126 d included in the bottom second coding unit 1120 b in the horizontal direction.

Referring to FIG. 11 , the third coding units 1116 a, 1116 b, 1116 c, 1116 d, 1126 a, 1126 b, 1126 c, and 1126 d having square shapes may be determined when each of the second coding units 1110 a, 1110 b, 1120 a, and 1120 b are split. The second coding units 1110 a and 1110 b determined when the first coding unit 1100 is split in the vertical direction and the second coding units 1120 a and 1120 b determined when the first coding unit 1100 is split in the horizontal direction have different shapes, but according to the third coding units 1116 a, 1116 b, 1116 c, 1116 d, 1126 a, 1126 b, 1126 c, and 1126 d determined thereafter, the first coding unit 1100 is split into coding units having the same shapes. Accordingly, even when coding units having the same shape are determined as a result by recursively splitting coding units through different processes based on at least one of block shape information and split shape information, the image decoding device 150 may process, in different orders, the coding units having the same shape.

FIG. 12 illustrates a process of determining a depth of a coding unit as a shape and size of the coding unit change, when the coding unit is recursively split and thus a plurality of coding units are determined, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine a depth of a coding unit according to a predetermined criterion. For example, the predetermined criterion may be a length of a longer side of the coding unit. When a length of a longer side of a coding unit before being split is 2n times a length of a longer side of a current coding unit, wherein n>0, the image decoding device 150 may determine that a depth of the current coding unit is higher than a depth of the coding unit before being split by n. Hereinafter, a coding unit having a higher depth will be referred to as a coding unit of a lower depth.

Referring to FIG. 12 , according to an embodiment, the image decoding device 150 may determine a second coding unit 1202 and a third coding unit 1204 of lower depths by splitting a first coding unit 1200 having a square shape, based on block shape information indicating a square shape (for example, block shape information may indicate ‘0: SQUARE’). When a size of the first coding unit 1200 having a square shape is 2N×2N, the second coding unit 1202 determined by splitting a width and a height of the first coding unit 1200 by ½ may have a size of N×N. In addition, the third coding unit 1204 determined by splitting a width and a height of the second coding unit 1202 by ½ may have a size of N/2×N/2. In this case, a width and a height of the third coding unit 1204 correspond to ½ times those of the first coding unit 1200. When a depth of the first coding unit 1200 is D, a depth of the second coding unit 1202, which is ½ times the width and height of the first coding unit 1200, may be D+1, and a depth of the third coding unit 1204, which is ½ times the width and height of the first coding unit 1200, may be D+2.

According to an embodiment, the image decoding device 150 may determine a second coding unit 1212 or 1222 and a third coding unit 1214 or 1224 of lower depths by splitting a first coding unit 1210 or 1220 having a non-square shape, based on block shape information indicating a non-square shape (for example, the block shape information may indicate ‘1: NS_VER’ indicating that a height is longer than a width or indicate ‘2: NS_HOR’ indicating that a width is longer than a height).

The image decoding device 150 may determine second coding units (for example, the second coding units 1202, 1212, 1222, and the like) by splitting at least one of the width and the height of the first coding unit 1210 having a size of N×2N. In other words, the image decoding device 150 may determine the second coding unit 1202 having a size of N×N or the second coding unit 1222 having a size of N×N/2 by splitting the first coding unit 1210 in a horizontal direction, or may determine the second coding unit 1212 having a size of N/2×N by splitting the first coding unit 1210 in horizontal and vertical directions.

According to an embodiment, the image decoding device 150 may determine the second coding units (for example, the second coding units 1202, 1212, 1222, and the like) by splitting at least one of the width and the height of the first coding unit 1220 having a size of 2N×N. That is, the image decoding device 150 may determine the second coding unit 1202 having a size of N×N or the second coding unit 1212 having a size of N/2×N by splitting the first coding unit 1220 in the vertical direction, or may determine the second coding unit 1222 having a size of N×N/2 by splitting the first coding unit 1220 in the horizontal and vertical directions.

According to an embodiment, the image decoding device 150 may determine third coding units (for example, the third coding units 1204, 1214, 1224, and the like) by splitting at least one of a width and a height of the second coding unit 1202 having a size of N×N. That is, the image decoding device 150 may determine the third coding unit 1204 having a size of N/2×N/2, the third coding unit 1214 having a size of N/2×N/2, or the third coding unit 1224 having a size of N/2×N/2 by splitting the second coding unit 1202 in vertical and horizontal directions.

According to an embodiment, the image decoding device 150 may determine the third coding units (for example, the third coding units 1204, 1214, 1224, and the like) by splitting at least one of a width and a height of the second coding unit 1212 having a size of N/2×N. That is, the image decoding device 150 may determine the third coding unit 1204 having a size of N/2×N/2 or the third coding unit 1224 having a size of N/2×N/2 by splitting the second coding unit 1212 in a horizontal direction, or determine the third coding unit 1214 having a size of N/2×N/2 by splitting the second coding unit 1212 in vertical and horizontal directions.

According to an embodiment, the image decoding device 150 may determine the third coding units (for example, the third coding units 1204, 1214, 1224, and the like) by splitting at least one of a width and a height of the second coding unit 1214 having a size of N×N/2. That is, the image decoding device 150 may determine the third coding unit 1204 having a size of N/2×N/2 or the third coding unit 1214 having a size of N/2×N/2 by splitting the second coding unit 1212 in a vertical direction, or determine the third coding unit 1224 having a size of N/2×N/2 by splitting the second coding unit 1212 in vertical and horizontal directions.

According to an embodiment, the image decoding device 150 may split coding units having square shapes (for example, the first coding units 1200, 1202, and 1204) in a horizontal or vertical direction. For example, the first coding unit 1200 having a size of 2N×2Nmay be split in the vertical direction to determine the first coding unit 1210 having a size of N×2N or in the horizontal direction to determine the first coding unit 1220 having a size of 2N×N/. According to an embodiment, when a depth is determined based on a length of a longest side of a coding unit, a depth of a coding unit determined when the first coding unit 1200, 1202, or 1204 is split in the horizontal or vertical direction may be the same as a depth of the first coding unit 1200, 1202, or 1204.

According to an embodiment, the width and height of the third coding unit 1214 or 1224 may be ½ times the first coding unit 1210 or 1220. When the depth of the first coding unit 1210 or 1220 is D, the depth of the second coding unit 1212 or 1214, which is ½ times the width and height of the first coding unit 1210 or 1220, may be D+1, and the depth of the third coding unit 1214 or 1224, which is ½ times the width and height of the first coding unit 1210 or 1220, may be D+2.

FIG. 13 illustrates a depth determinable according to shapes and sizes of coding units, and a part index (PID) for distinguishing between the coding units, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine second coding units having various shapes by splitting a first coding unit 1300 having a square shape. Referring to FIG. 13 , the image decoding device 150 may determine second coding units 1302 a, 1302 b, 1304 a, 1304 b, 1306 a, 1306 b, 1306 c, and 1306 d by splitting the first coding unit 1300 in at least one of a vertical direction and a horizontal direction, according to split shape information. That is, the image decoding device 150 may determine the second coding units 1302 a, 1302 b, 1304 a, 1304 b, 1306 a, 1306 b, 1306 c, and 1306 d based on split shape information about the first coding unit 1300.

According to an embodiment, depths of the second coding units 1302 a, 1302 b, 1304 a, 1304 b, 1306 a, 1306 b, 1306 c, and 1306 d determined according to the split shape information about the first coding unit 1300 having a square shape may be determined based on lengths of longer sides. For example, because lengths of longer sides of the second coding units 1302 a, 1302 b, 1304 a, and 1304 b having non-square shapes are the same as a length of one side of the first coding unit 1300 having a square shape, depths of the first coding unit 1300 and the second coding units 1302 a, 1302 b, 1304 a, and 1304 b having non-square shapes may be D, i.e., the same. On the other hand, when the image decoding device 150 splits the first coding unit 1300 into the four second coding units 1306 a, 1306 b, 1306 c, and 1306 d having square shapes based on split shape information, because a length of one side of each of the second coding units 1306 a, 1306 b, 1306 c, and 1306 d having square shapes is ½ of a length of one side of the first coding unit 1300, depths of the second coding units 1306 a, 1306 b, 1306 c, and 1306 d may be D+1, i.e., one depth lower than the depth D of the first coding unit 1300.

According to an embodiment, the image decoding device 150 may split a first coding unit 1310 having a height longer than a width into a plurality of second coding units 1312 a, 1312 b, 1314 a, 1314 b, and 1314 c by splitting the first coding unit 1310 in a horizontal direction according to split shape information. According to an embodiment, the image decoding device 150 may split a first coding unit 1320 having a width longer than a height into a plurality of second coding units 1322 a and 1322 b, or 1324 a, 1324 b, and 1324 c by splitting the first coding unit 1320 in a vertical direction according to split shape information.

According to an embodiment, depths of the second coding units 1312 a, 1312 b, 1314 a, 1314 b, 1316 a, 1316 b, 1316 c, and 1316 d determined according to the split shape information about the first coding unit 1310 or 1320 having a non-square shape may be determined based on lengths of longer sides. For example, because a length of one side of each of the second coding units 1312 a and 1312 b having square shapes is ½ of a length of one side of the first coding unit 1310 having a non-square shape in which a height is longer than a width, the depths of the second coding units 1302 a, 1302 b, 1304 a, and 1304 b having square shapes are D+1, i.e., one depth lower than the depth D of the first coding unit 1310 having a non-square shape.

In addition, the image decoding device 150 may split the first coding unit 1310 having a non-square shape into an odd number of the second coding units 1314 a, 1314 b, and 1314 c based on split shape information. The odd number of second coding units 1314 a, 1314 b, and 1314 c may include the second coding units 1314 a and 1314 c having non-square shapes and the second coding unit 1314 b having a square shape. Here, because lengths of longer sides of the second coding units 1314 a and 1314 c having non-square shapes and a length of one side of the second coding unit 1314 b having a square shape are 1/2 of a length of one side of the first coding unit 1310, depths of the second coding units 1314 a, 1314 b, and 1314 c may be D+1, i.e., one depth lower than the depth D of the first coding unit 1310. The image decoding device 150 may determine depths of coding units related to the first coding unit 1310 having a non-square shape in which a width is longer than a height in the similar manner as depths of coding units related to the first coding unit 1310 are determined.

According to an embodiment, while determining PIDs for distinguishing between coding units, the image decoding device 150 may determine the PIDs based on size ratios between the coding units when an odd number of the coding units do not have the same size. Referring to FIG. 13 , the coding unit 1314 b located at the center of the odd number of coding units 1314 a, 1314 b, and 1314 c has the same width as the coding units 1314 a and 1314 c, but has a height twice higher than heights of the coding units 1314 a and 1314 c. In this case, the coding unit 1314 b located at the center may include two of each of the coding units 1314 a and 1314 c. Accordingly, when a PID of the coding unit 1314 b located at the center according to a scan order is 1, a PID of the coding unit 1314 c located in a next order may be increased by 2, i.e., 3. That is, values of PIDs may be discontinuous. According to an embodiment, the image decoding device 150 may determine whether coding units split into an odd number have the same size based on discontinuity of PIDs for distinguishing between the coding units.

According to an embodiment, the image decoding device 150 may determine whether a plurality of coding units determined when a current coding unit is split have certain split shapes based on values of PIDs for distinguishing between the coding units. Referring to FIG. 13 , the image decoding device 150 may determine an even number of the coding units 1312 a and 1312 b or an odd number of the coding units 1314 a, 1314 b, and 1314 c by splitting the first coding unit 1310 having a rectangular shape in which a height is longer than a width. The image decoding device 150 may use an ID indicating each coding unit so as to distinguish between a plurality of coding units. According to an embodiment, the PID may be obtained from a sample at a predetermined location (for example, an upper-left sample) of each coding unit.

According to an embodiment, the image decoding device 150 may determine a coding unit at a predetermined location from among coding units determined via split, by using PIDs for distinguishing between the coding units. According to an embodiment, when split shape information about the first coding unit 1310 having a rectangular shape in which a height is longer than a width indicates a split into three coding units, the image decoding device 150 may split the first coding unit 1310 into the three coding units 1314 a, 1314 b, and 1314 c. The image decoding device 150 may allocate a PID to each of the three coding units 1314 a, 1314 b, and 1314 c. The image decoding device 150 may compare PIDs of coding units so as to determine a center coding unit from among an odd number of coding units. The image decoding device 150 may determine the coding unit 1314 b having a PID corresponding to a center value from among PIDs as a coding unit located at the center from among coding units determined when the first coding unit 1310 is split, based on PIDs of the coding units. According to an embodiment, the image decoding device 150 may determine PIDs based on size ratios between coding units when the coding units do not have the same size, while determining the PIDs for distinguishing between the coding units. Referring to FIG. 13 , the coding unit 1314 b generated when the first coding unit 1310 is split may have the same width as the coding units 1314 a and 1314 c, but may have a height twice higher than heights of the coding units 1314 a and 1314 c. In this case, when the PID of the coding unit 1314 b located at the center is 1, the PID of the coding unit 1314 c located in a next order may be increased by 2, i.e., 3. As such, when an increase range changes while PIDs are uniformly increasing, the image decoding device 150 may determine that a coding unit is split into a plurality of coding units including a coding unit having a different size from other coding units. According to an embodiment, when split shape information indicates a split into an odd number of coding units, the image decoding device 150 may split a current coding unit into an odd number of coding units in which a coding unit at a predetermined location (for example, a center coding unit) has a different size from other coding units. In this case, the image decoding device 150 may determine the center coding unit having the different size by using PIDs of the coding units. However, because the PID, and a size or location of a coding unit at a predetermined location are specified to describe an embodiment, and thus the present disclosure should not be construed as being limited thereto, and various PIDs, and various locations and sizes of a coding unit may be used.

According to an embodiment, the image decoding device 150 may use a predetermined data unit from which a coding unit starts to be recursively split.

FIG. 14 illustrates that a plurality of coding units are determined according to a plurality of predetermined data units included in a picture, according to an embodiment.

According to an embodiment, a predetermined data unit may be defined as a data unit from which a coding unit starts to be recursively split by using at least one of block shape information and split shape information. That is, the predetermined data unit may correspond to a coding unit of an uppermost depth used in a process of determining a plurality of coding units split from a current picture. Hereinafter, for convenience of description, such a predetermined data unit is referred to as a reference data unit.

According to an embodiment, a reference data unit may indicate a predetermined size and shape. According to an embodiment, a reference coding unit may include M×N samples. Here, M and N may be equal to each other, and may be an integer expressed as a multiple of 2. That is, the reference data unit may indicate a square shape or a non-square shape, and may later be split into an integer number of coding units.

According to an embodiment, the image decoding device 150 may split a current picture into a plurality of reference data units. According to an embodiment, the image decoding device 150 may split the plurality of reference data units obtained by splitting the current picture by using split information about each of the reference data units. Split processes of such reference data units may correspond to split processes using a quad-tree structure.

According to an embodiment, the image decoding device 150 may pre-determine a smallest size available for the reference data unit included in the current picture. Accordingly, the image decoding device 150 may determine the reference data unit having various sizes that are equal to or larger than the smallest size, and may determine at least one coding unit based on the determined reference data unit by using block shape information and split shape information.

Referring to FIG. 14 , the image decoding device 150 may use a reference coding unit 1400 having a square shape, or may use a reference coding unit 1402 having a non-square shape. According to an embodiment, a shape and size of a reference coding unit may be determined according to various data units (for example, a sequence, a picture, a slice, a slice segment, and a largest coding unit) that may include at least one reference coding unit.

According to an embodiment, the receiver 160 of the image decoding device 150 may obtain, from a bitstream, at least one of information about a shape of a reference coding unit and information about a size of the reference coding unit, according to the various data units. Processes of determining at least one coding unit included in the reference coding unit 1400 having a square shape have been described above through processes of splitting the current coding unit 1000 of FIG. 10 , and processes of determining at least one coding unit included in the reference coding unit 1402 having a non-square shape have been described above through processes of splitting the current coding unit 1100 of FIG. 11 , and thus descriptions thereof are not provided here.

According to an embodiment, to determine a size and shape of a reference coding unit according to some data units pre-determined based on a predetermined condition, the image decoding device 150 may use a PID for checking the size and shape of the reference coding unit. That is, the receiver 160 may obtain, from a bitstream, only a PID for checking a size and shape of a reference coding unit as a data unit satisfying a predetermined condition (for example, a data unit having a size equal to or smaller than a slice) from among various data units (for example, a sequence, a picture, a slice, a slice segment, and a largest coding unit), according to slices, slice segments, and largest coding units. The image decoding device 150 may determine the size and shape of the reference data unit according to data units that satisfy the predetermined condition, by using the PID. When information about a shape of a reference coding unit and information about a size of a reference coding unit are obtained from a bitstream and used according to data units having relatively small sizes, usage efficiency of the bitstream may not be sufficient, and thus instead of directly obtaining the information about the shape of the reference coding unit and the information about the size of the reference coding unit, only a PID may be obtained and used. In this case, at least one of the size and the shape of the reference coding unit corresponding to the PID indicating the size and shape of the reference coding unit may be pre-determined. That is, the image decoding device 150 may select at least one of the pre-determined size and shape of the reference coding unit according to the PID so as to determine at least one of the size and shape of the reference coding unit included in a data unit that is a criterion for obtaining the PID.

According to an embodiment, the image decoding device 150 may use at least one reference coding unit included in one largest coding unit. That is, a largest coding unit splitting an image may include at least one reference coding unit, and a coding unit may be determined when each of the reference coding unit is recursively split. According to an embodiment, at least one of a width and height of the largest coding unit may be an integer times at least one of a width and height of the reference coding unit. According to an embodiment, a size of a reference coding unit may be equal to a size of a largest coding unit, which is split n times according to a quad-tree structure. That is, the image decoding device 150 may determine a reference coding unit by splitting a largest coding unit n times according to a quad-tree structure, and may split the reference coding unit based on at least one of block shape information and split shape information according to various embodiments.

FIG. 15 illustrates a processing block that is a criterion in determining a determining order of a reference coding unit included in a picture 1500, according to an embodiment.

According to an embodiment, the image decoding device 150 may determine at least one processing block splitting a picture. A processing block is a data unit including at least one reference coding unit splitting an image, and the at least one reference coding unit included in the processing block may be determined in a certain order. That is, a determining order of the at least one reference coding unit determined in each processing block may correspond to one of various orders for determining a reference coding unit, and may vary according to processing blocks. A determining order of a reference coding unit determined per processing block may be one of various orders, such as a raster scan order, a Z-scan order, an N-scan order, an up-right diagonal scan order, a horizontal scan order, and a vertical scan order, but should not be limitedly interpreted by the scan orders.

According to an embodiment, the image decoding device 150 may determine a size of at least one processing block included in an image by obtaining information about a size of a processing block. The image decoding device 150 may obtain, from a bitstream, the information about a size of a processing block to determine the size of the at least one processing block included in the image. The size of the processing block may be a predetermined size of a data unit indicated by the information about the size of the processing block.

According to an embodiment, the receiver 160 of the image decoding device 150 may obtain, from the bitstream, the information about a size of a processing block according to certain data units. For example, the information about a size of a processing block may be obtained from the bitstream in data units of images, sequences, pictures, slices, and slice segments. That is, the receiver 160 may obtain, from the bitstream, the information about a size of a processing block according to such several data units, and the image decoding device 150 may determine the size of at least one processing block splitting the picture by using the obtained information about a size of a processing block, wherein the size of the processing block may be an integer times a size of a reference coding unit.

According to an embodiment, the image decoding device 150 may determine sizes of processing blocks 1502 and 1512 included in the picture 1500. For example, the image decoding device 150 may determine a size of a processing block based on information about a size of a processing block, the information obtained from a bitstream. Referring to FIG. 15 , the image decoding device 150 may determine horizontal sizes of the processing blocks 1502 and 1512 to be four times a horizontal size of a reference coding unit, and a vertical size thereof to be four times a vertical size of the reference coding unit, according to an embodiment. The image decoding device 150 may determine a determining order of at least one reference coding unit in at least one processing block.

According to an embodiment, the image decoding device 150 may determine each of the processing blocks 1502 and 1512 included in the picture 1500 based on a size of a processing block, and may determine a determining order of at least one reference coding unit included in each of the processing blocks 1502 and 1512. According to an embodiment, determining of a reference coding unit may include determining of a size of the reference coding unit.

According to an embodiment, the image decoding device 150 may obtain, from a bitstream, information about a determining order of at least one reference coding unit included in at least one processing block, and may determine the determining order of the at least one reference coding unit based on the obtained information about a determining order. The information about a determining order may be defined as an order or direction of determining reference coding units in a processing block. That is, an order of determining reference coding units may be independently determined per processing block.

According to an embodiment, the image decoding device 150 may obtain, from a bitstream, information about a determining order of a reference coding unit according to certain data units. For example, the receiver 160 may obtain, from the bitstream, the information about a determining order of a reference coding unit according to data units, such as images, sequences, pictures, slices, slice segments, processing blocks, or the like. Because the information about a determining order of a reference coding unit indicates a determining order of a reference coding unit in a processing block, the information about a determining order may be obtained per certain data unit including an integer number of processing blocks.

According to an embodiment, the image decoding device 150 may determine at least one reference coding unit based on the determined order.

According to an embodiment, the receiver 160 may obtain, from the bitstream, information about a determining order of a reference coding unit, as information related to the processing blocks 1502 and 1512, and the image decoding device 150 may determine an order of determining at least one reference coding unit included in the processing blocks 1502 and 1512 and may determine at least one reference coding unit included in the picture 1500 according to a determining order of a coding unit. Referring to FIG. 15 , the image decoding device 150 may determine determining orders 1504 and 1514 of at least one reference coding unit respectively related to the processing blocks 1502 and 1512. For example, when information about a determining order of a reference coding unit is obtained per processing block, determining orders of a reference coding unit related to the processing blocks 1502 and 1512 may be different from each other. When the determining order 1504 related to the processing block 1502 is a raster scan order, reference coding units included in the processing block 1502 may be determined according to the raster scan order. On the other hand, when the determining order 1514 related to the processing block 1512 is an inverse order of the raster scan order, reference coding units included in the processing block 1512 may be determined in the inverse order of the raster scan order. With reference to FIGS. 1 to 15 , the method of splitting an image into largest coding units, and splitting each largest coding unit into coding units having a hierarchical tree structure are described above. With reference to FIGS. 16 to 25 , it will now be described how to encode or decode the encoding units of the same depth according to which coding order.

FIG. 16 illustrates a video decoding device 1600 involving determining whether to split a current block and an encoding order of split lower blocks, according to an embodiment.

The video decoding device 1600 includes a block splitter 1610, an encoding order determiner 1620, a prediction method determiner 1630, and a block decoder 1640. In FIG. 16 , the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 are formed as separate elements, but in another embodiment, the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 may be integrated to be implemented as one element.

In FIG. 16 , the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 are seen as elements located within one apparatus, but the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 are not required to be physically adjacent to each other. Thus, in another embodiment, the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 may be dispersed.

According to an embodiment, the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 may be implemented by one processor. In another embodiment, the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 may be implemented by a plurality of processors.

Functions performed by the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 of FIG. 16 may be performed by the decoder 180 of FIG. 1B.

The block splitter 1610 may obtain split information indicating whether a current block is to be split. The split information indicates whether the current block is to be split into at least two smaller blocks. When the split information indicates that the current block is to be split, the block splitter 1610 splits the current block into at least two lower blocks.

The current block may be split into various shapes according to a shape of the current block. For example, when the current block has a square shape, the current block may be split into at least four square lower blocks, according to the split information.

When at least two split methods are allowed for the shape of the current block, the block splitter 1610 may select a split method according to split shape information. Thus, when the split information indicates that the current block is to be split, the block splitter 1610 may split the current block, according to the split method indicated by the split shape information.

For example, when the current block has a square shape of 2N×2Nsize, the split shape information may indicate a split method from among N×N split, 2N×N split, N×2N split, vertically unequal tri-split, and horizontally unequal tri-split, the split method being applied to the current block. The N×N split indicates a method of splitting the current block into four blocks of N×N size. The 2N×N split indicates a method of splitting the current block into blocks of 2N×N size. The N×2N split indicates a method of splitting the current block into blocks of N×2N size. The vertically unequal tri-split indicates a method of splitting a 2N×2N-size block into three blocks that have a same width and have respective heights having a ratio 1:2:1. The horizontally unequal tri-split indicates a method of splitting a 2N×2N-size block into three blocks that have a same height and have respective heights having a ratio 1:2:1. In addition, the current block may be split according to one of various horizontal split methods or vertical split methods.

When the current block has a vertically-long rectangular shape having 2N×N size, the split shape information may indicate a split method from among N×N split and vertically unequal tri-split, the split method being applied to the current block. The N×N split indicates a method of splitting the current block into two blocks of N×N size. The vertically unequal tri-split indicates a method of splitting a 2N×N-size block into three blocks that have a same width and have respective heights having a ratio 1:2:1. In addition, the current block may be split according to one of various horizontal split methods or vertical split methods.

When the current block has a horizontally-long rectangular shape having N×2N size, the split shape information may indicate a split method from among N×N split and horizontally unequal tri-split, the split method being applied to the current block. The N×N split indicates a method of splitting the current block into two blocks of N×N size. The horizontally unequal tri-split indicates a method of splitting a N×2N-size block into three blocks that have a same height and have respective heights having a ratio 1:2:1. In addition, the current block may be split according to one of various horizontal split methods or vertical split methods.

In addition to the aforementioned split methods, a method of asymmetrically splitting a current block, a method of splitting a current block according to a triangular shape, a method of splitting a current block according to other geometric shape, or the like may be used to split a current block having a square shape and or a rectangular shape.

When the split information indicates that the current block is not to be split, the block splitter 1610 does not split the current block. Then, the block decoder 1640 decodes the current block.

When the current block is a coding unit, the block splitter 1610 determines the current block as a final coding unit. The final coding unit is not split into coding units having a deeper depth. According to an embodiment, when the current block that is the final coding unit is split into data units other than a coding unit, the block decoder 1640 may make the block splitter 1610 split the current block.

According to an embodiment, the block splitter 1610 may split the current block into one or more prediction units according to a hierarchical tree structure. Equally, the block splitter 1610 may split the current block may split the current block into one or more transform units according to the hierarchical tree structure. Then, the block decoder 1640 may reconstruct the current block according to a prediction result with respect to the prediction units and a transformation result with respect to the transform units.

When the current block is a prediction unit, the block decoder 1640 may perform prediction on the current block. When the current block is a transform unit, the block decoder 1640 may inverse quantize and inverse transform a quantized transform coefficient with respect to the current block, thereby obtaining residual data.

The encoding order determiner 1620 obtains encoding order information indicating an encoding order of lower blocks. Then, the encoding order determiner 1620 may determine a decoding order of the lower blocks, based on the obtained encoding order information.

The encoding order information indicates an encoding order of at least two lower blocks included in the current block. A data amount of the encoding order information is determined based on the number of lower blocks and an encoding order determining scheme.

For example, when there are two lower blocks, the encoding order information may be determined to indicate a first-encoded lower block from among the two lower blocks. Thus, the encoding order information may be in the form of a flag having a 1-bit data amount.

However, when there are four lower blocks, the number of cases of an encoding order of lower blocks is 4!=24. Therefore, to indicate 24 encoding orders, a 5-bit data amount is required. That is, when the number of lower blocks is increased, the number of cases of an encoding order is increased. Therefore, to decrease a data amount of the encoding order information, an encoding order determining scheme of determining an encoding order by determining whether encoding orders of some lower block pairs are swapped in a predetermined default encoding order. Encoding order information indicating whether the encoding orders of some lower block pairs are to be swapped indicates a forward direction or a backward direction with respect to the default encoding order.

A current picture including the current block is encoded and decoded according to the default encoding order. All blocks and pixels to be encoded and decoded in the current picture are to be encoded and decoded at a same level according to the default encoding order. Thus, lower blocks at a same level split from the current block are also to be encoded and decoded according to the default encoding order. An embodiment of the default encoding order is illustrated in FIGS. 17A to 17C to be described below.

Therefore, when a lower block pair is encoded according to the default encoding order, it is described that the lower block pair is encoded in a forward direction. On the contrary, when the lower block pair is encoded according to an inverse order to the default encoding order, it is described that the lower block pair is encoded in a backward direction.

For example, in a case where two lower blocks are horizontally adjacent to each other and are encoded in a forward direction, the encoding order information may be determined to allow a left lower block to be first decoded. On the contrary, in a case where the two lower blocks that are horizontally adjacent to each other are encoded in a backward direction, the encoding order information may be determined to allow a right lower block to be first decoded.

Equally, in a case where two lower blocks are vertically adjacent to each other and are encoded in a forward direction, the encoding order information may be determined to allow an upper-lower block to be first decoded. On the contrary, in a case where the two lower blocks that are vertically adjacent to each other are encoded in a backward direction, the encoding order information may be determined to allow a further lower block to be first decoded.

When the encoding order information indicates only an encoding order of a lower block pair, the encoding order information has a 1-bit data amount. The encoding order information having 1-bit data amount may be defined as an encoding order flag.

The encoding order determiner 1620 may obtain the encoding order information from a bitstream. The encoding order information may be positioned after split information in the bitstream.

The encoding order determiner 1620 may internally determine the encoding order information according to a surrounding environment of the current block. The encoding order information may be determined according to whether neighboring blocks adjacent to the current block have been encoded. For example, the encoding order determiner 1620 may determine a lower block to be first decoded, the lower block having many adjacent neighboring blocks from among lower blocks.

With respect to the encoding order determiner 1620, a default encoding order according to an embodiment will now be described with reference to FIGS. 17A to 17C. The default encoding order of FIGS. 17A to 17C is a Z encoding order. According to the Z encoding order, data units are encoded from the left to the right, and when data units of a current row are all encoded, data units included in a lower row of the current row are encoded from the left to the right. The aforementioned Z encoding order is referred to as a raster scan order.

FIG. 17A illustrates encoding orders according to a Z encoding order of largest coding units included in a current picture 1700. According to the Z encoding order, indexes 0 to 15 are set to the largest coding units. Largest coding units of a first row to which the indexes 0 to 3 are set according to the Z encoding order are first encoded, and largest coding units of a second row to which the indexes 4 to 7 are encoded from the left to the right. The largest coding units are internally encoded according to the Z encoding order.

FIG. 17B illustrates an encoding order of a largest coding unit 1710 having the index 6 from among the largest coding units included in the current picture 1700. Coding units of a final depth for which split has been completed according to the Z encoding order are set with the indexes 0 to 15. The Z encoding order is applied to data units of a same depth. In addition, until lower coding units of a coding unit of a depth n are all encoded, the coding unit of the depth n having a second priority is not encoded. For example, until coding units having the indexes 5 to 14 are all encoded, a coding unit having the index 15 is not encoded. The coding units are also internally encoded according to the Z encoding order.

FIG. 17C illustrates a reference sample to be referred to for a coding unit 1724 having the index 6 from among the coding units included in the largest coding unit 1710. Only a coding unit 1712 having the index 0 and a coding unit 1722 having the index 5 have been reconstructed around the coding unit 1724 having the index 6 to be currently encoded. Therefore, for the coding unit 1724, only a pixel 1750 of the coding unit 1712 and a pixel 1760 of the coding unit 1722 may be used as a reference sample.

The Z encoding order of FIGS. 17A to 17C may be applied in another direction according to a data unit. For example, the Z encoding order may be changed to allow data units to be encoded from the right to the left in a same row. Also, the Z encoding order may be changed such that, after all data units of a current row are encoded, data units included in an upper row of the current row are to be encoded. Also, the Z encoding order may be changed such that data units of a same column are encoded from the top to the bottom and, after all data units of a current column are encoded, data units included in a right column of the current column are to be encoded.

Regarding the encoding order determiner 1620, FIGS. 18A and 18B respectively illustrate a case 1800 in which a coding unit 1810 is encoded in a forward direction and a case 1802 in which a coding unit 1820 is encoded in a backward direction. With reference to FIGS. 18A and 18B, an advantage obtained by changing an encoding order will now be described.

The coding units 1810 and 1820 of FIGS. 18A and 18B are predicted according to an intra mode in an upper-right direction. A continuous line 1830 of FIGS. 18A and 18B corresponds to pixels having a constant value and arranged in a straight line in an original image. Therefore, when a current coding unit is predicted in a direction of the continuous line 1830, prediction accuracy with respect to the coding units 1810 and 1820 may be improved.

In the case 1800 of encoding in the forward direction, a left coding unit, an upper coding unit, and an upper-right coding unit of the current coding unit 1810 are first reconstructed prior to the current coding unit 1810. Therefore, the current coding unit 1810 refers to pixels or encoding information of the left coding unit, the upper coding unit, and the upper-right coding unit. For example, pixels 1816 located a lower corner of the upper-right coding unit are used in predicting the current coding unit 1810. Because the pixels 1816 are spatially distant from the current coding unit 1810, prediction accuracy with respect to a portion 1814 of the current coding unit 1810 may be low.

However, in the case 1802 of encoding in the backward direction, a right coding unit, an upper coding unit, and an upper-left coding unit of a current coding unit 1820 are first reconstructed before the current coding unit 1820, and thus, in intra prediction, pixels 1826 located at a left corner of the right coding unit may be used in predicting the current coding unit 1820. Because the pixels 1826 are adjacent to the current coding unit 1820, prediction accuracy with respect to a portion 1824 of the current coding unit 1820 may be further improved than the prediction accuracy with respect to the portion 1814 of the current coding unit 1810.

As in an embodiment of the intra prediction described with reference to FIGS. 18A and 18B, there are many cases in which prediction accuracy of inter prediction may be improved by obtaining encoding information from a block located in a backward direction. When a current coding unit and a right coding unit of the current coding unit are coding units with respect to a same object, the current coding unit and motion information of the right coding unit may be similar to each other. Therefore, coding efficiency may be increased by deriving motion information of the current coding unit from the motion information of the right coding unit.

Therefore, by determining an encoding order by comparing coding efficiency of a case in which the current coding unit is encoded in a forward direction with coding efficiency of a case in which the current coding unit is encoded in a backward direction, coding efficiency with respect to an image may be improved.

Encoding order information may be set to be equal to encoding order information applied to an upper block of a current block. For example, when the current block is a prediction unit or a transform unit, the encoding order determiner 1620 may apply, to the current block, encoding order information applied to a coding unit including the current block. As another example, when the current block is a coding unit, the encoding order determiner 1620 may apply, to the current block, encoding order information applied to a coding unit whose depth is lower than the current block.

When at least two encoding order flags are present with respect to the current block, the encoding order determiner 1620 may obtain only one encoding order flag from a bitstream, and may determine the other encoding order flag to interoperate with the encoding order flag obtained from the bitstream.

With respect to encoding order determination by the encoding order determiner 1620, FIG. 19 illustrates a tree structure of a largest coding unit for describing an encoding order of the largest coding unit and coding units included in the largest coding unit.

A largest coding unit 1950 is split into a plurality of coding units 1956, 1958, 1960, 1962, 1968, 1970, 1972, 1974, 1980, 1982, 1984, and 1986. The largest coding unit 1950 corresponds to an uppermost node 1900 of the tree structure. The plurality of coding units 1956, 1958, 1960, 1962, 1968, 1970, 1972, 1974, 1980, 1982, 1984, and 1986 respectively correspond to a plurality of nodes 1906, 1908, 1910, 1912, 1918, 1920, 1922, 1924, 1930, 1932, 1934, and 1936. Upper encoding order flags 1902, 1914, and 1926 indicating encoding orders in the tree structure correspond to arrows 1952, 1964, and 1976, and upper encoding order flags 1904, 1916, and 1928 correspond to arrows 1954, 1966, and 1978.

An upper encoding order flag indicates an encoding order of two coding units located above from among four coding units having a same depth. When the upper encoding order flag indicates 0, encoding is performed in a forward direction. On the contrary, when the upper encoding order flag indicates 1, encoding is performed in a backward direction.

Equally, a lower encoding order flag indicates an encoding order of two coding units located in the lower side from among the four coding units having the same depth. When the lower encoding order flag indicates 0, encoding is performed in a forward direction. On the contrary, when the lower encoding order flag indicates 1, encoding is performed in a backward direction.

For example, because an upper encoding order flag 1914 indicates 0, an encoding order between coding units 1968 and 1970 is determined to be from the left that is a forward direction to the right. Also, because a lower encoding order flag 1916 indicates 0, an encoding order between coding units 1972 and 1974 is determined to be from the right that is a backward direction to the left.

According to an embodiment, it may be set for an upper encoding order flag and a lower encoding order flag to have a same value. For example, when the upper encoding order flag 1902 is determined to be 1, the lower encoding order flag 1904 corresponding to the upper encoding order flag 1902 may be determined to be 1. Because values of the upper encoding order flag and the lower encoding order flag are determined to be 1 bit, information amount of encoding order information is decreased.

According to an embodiment, an upper encoding order flag and a lower encoding order flag of a current coding unit may be determined by referring to at least one of an upper encoding order flag and a lower encoding order flag applied to a coding unit having a depth lower than the current coding unit. For example, the upper encoding order flag 1926 and the lower encoding order flag 1928 applied to the coding units 1980, 1982, 1984, and 1986 may be determined based on the lower encoding order flag 1916 applied to the coding units 1972 and 1974. Therefore, the upper encoding order flag 1926 and the lower encoding order flag 1928 may be determined to have a same value as the lower encoding order flag 1916. Because values of the upper encoding order flag and the lower encoding order flag are determined from an upper coding unit of the current coding unit, encoding order information is not obtained from a bitstream. Therefore, information amount of the encoding order information is decreased.

With respect to encoding order determination by the encoding order determiner 1620, how an encoding order of at least three blocks arranged in a vertical or horizontal direction is changed according to an encoding order flag will now be described with reference to FIGS. 20A and 20B.

An embodiment of FIG. 20A is about a method of swapping encoding orders, based on an encoding order flag, only when the encoding orders of spatially-neighboring coding units are adjacent to each other.

A coding unit 2000 is split into three coding units 2010, 2020, and 2030. When a default encoding order is from the left to the right, encoding is performed in order of the coding unit 2010, the coding unit 2020, and the coding unit 2030. However, an encoding order may be changed according to encoding order flags 2040 and 2050.

The encoding order flag 2040 indicates an encoding order of the coding unit 2010 and the coding unit 2020. When the encoding order flag 2040 indicates 0, the encoding order of the coding unit 2010 and the coding unit 2020 is determined to be a forward direction. Therefore, the coding unit 2010 is encoded prior to the coding unit 2020. However, when the encoding order flag 2040 indicates 1, the encoding order of the coding unit 2010 and the coding unit 2020 is determined to be a backward direction, and thus the coding unit 2020 is encoded prior to the coding unit 2010.

The encoding order flag 2050 indicates an encoding order of the coding unit 2020 and the coding unit 2030. When the encoding order flag 2040 indicates a forward direction, the encoding order flag 2050 is obtained. When the encoding order flag 2040 indicates a backward direction, encoding orders of the coding unit 2020 and the coding unit 2030 are not adjacent to each other, and thus the encoding order flag 2050 is not obtained. When the encoding order flag 2050 indicates 0, an encoding order of the coding unit 2020 and the coding unit 2030 is determined to be a forward direction. Therefore, the coding unit 2020 is encoded prior to the coding unit 2030. However, when the encoding order flag 2050 indicates 1, an encoding order of the coding unit 2020 and the coding unit 2030 is determined to be a backward direction, and thus the coding unit 2030 is encoded prior to the coding unit 2020.

According to an embodiment of FIG. 20A, an encoding order of three coding units has three cases. Therefore, to determine the encoding order, one or two encoding order flags are used.

An embodiment of FIG. 20B is about a method of determining an encoding order, based on an encoding order flag 2060 indicating a direction of the encoding order to be applied to three coding units.

The encoding order flag 2060 indicates whether an encoding order is a forward direction or a backward direction. For example, when the encoding order flag 2060 indicates 0, an encoding order of the coding units 2010, 2020, and 2030 may be determined to be the forward direction. Therefore, when the encoding order flag 2060 indicates 0, encoding may be performed in order of the coding unit 2010, the coding unit 2020, and the coding unit 2030.

On the other hand, when the encoding order flag 2060 indicates 1, the encoding order of the coding units 2010, 2020, and 2030 may be determined to be the backward direction. Therefore, when the encoding order flag 2060 indicates 1, encoding may be performed in order of the coding unit 2030, the coding unit 2020, and the coding unit 2010.

Referring to the embodiment of FIG. 20B, the encoding order of three coding units has two cases. Therefore, to determine the encoding order, one encoding order flag is used.

The methods of determining an encoding order which are used in the embodiments of FIGS. 20A and 20B may be applied to at least four coding units.

The encoding order determiner 1620 may check encoding order change allowance information with respect to an upper data unit of a current block. The encoding order change allowance information indicates whether a change in an encoding order is allowable for blocks included in the upper data unit of the current block. When the encoding order change allowance information indicates that the change in the encoding order is not allowable, all blocks of the upper data unit are decoded according to a default encoding order. When the encoding order change allowance information indicates that encoding order information with respect to the current block has been encoded, the encoding order determiner 1620 may obtain the encoding order information.

The encoding order change allowance information may be included in a video parameter set, a sequence parameter set, a picture parameter set, a slice segment header, a header of a largest coding unit, or the like. When at least two types of the encoding order information are present, two pieces of encoding order change allowance information about at least two types of the encoding order information may be separately stored in different headers.

The encoding order change allowance information may indicate a depth at which encoding order information is provided, or a block size. For example, only when a depth of the current block is included in the depth indicated by the encoding order change allowance information, the encoding order determiner 1620 may obtain the encoding order information. As another example, only when a size of the current block corresponds to the block size indicated by the encoding order change allowance information, the encoding order determiner 1620 may obtain the encoding order information.

When split information indicates that the current block is not to be split, the prediction method determiner 1630 may determine a prediction method with respect to the current block according to encoding information of the current block and whether neighboring blocks of the current block have been decoded.

The encoding information of the current block may indicate how the current block is to be predicted. In detail, the encoding information may indicate a prediction method from among a plurality of intra prediction modes and inter prediction modes. The intra prediction modes that are applicable to the current block may include a directional mode, a DC mode, a planar mode, a multi-parameter intra (MPI) prediction mode, a linear-model (LM) chroma mode, a most probable chroma (MPC) mode, or the like. The inter prediction modes that are applicable to the current block may include a merge mode, an advanced motion vector prediction (AMVP) mode, an inter skip mode, an overlapped block motion compensation (OBMC) mode, a sub-block motion vector prediction (MVP) mode, an affine motion compensation (MC) mode, a frame rate up conversion (FRUC) mode, or the like. Therefore, the prediction method determiner 1630 may determine a prediction mode to be applied to the current block, based on the encoding information of the current block.

Whether the neighboring blocks of the current block have been decoded, a reference block and a reference sample to be referred to in predicting the current block may be determined. Referring to the raster scan described with reference to FIGS. 17A to 17C, only left, upper, upper-left, upper-right, and lower-left blocks in the current block may have been decoded prior to the current block. However, when an encoding tree block including the current block has been decoded by the encoding order determiner 1620 according to an encoding order different from the raster scan, a right block and a lower-right block of the current block may have been decoded prior to the current block. Therefore, the prediction method determiner 1630 may determine the reference block and the reference sample to be referred to in predicting the current block, according to whether the left, upper, upper-left, upper-right, lower-left, right, and lower-right blocks of the current block have been decoded.

When the current block is intra predicted, the prediction method determiner 1630 may determine reference samples to be referred to for the current block, according to whether the neighboring blocks of the current block have been decoded. In an intra prediction mode, prediction values of samples of the current block are determined by referring to sample values of samples adjacent to the current block. Therefore, only a neighboring block from among neighboring blocks of the current block may be used in predicting the current block, wherein the neighboring block has been decoded prior to the current block and may be referred to for the current block.

For example, when blocks are encoded according to a forward direction of the raster scan described with reference to FIGS. 17A to 17C, reference samples of the upper block, the left block, the upper-left block, the lower-left block, and the upper-right block of the current block may be used in predicting the current sample. On the contrary, when the blocks are encoded according to a backward direction to the raster scan, reference samples of the upper block, the right block, the upper-right block, the lower-right block, and the upper-left block of the current block may be used in predicting the current sample.

FIGS. 21A and 21B illustrate a method of transforming a current block when not a left block but a right block of the current block has been decoded prior to the current block.

When the current block that is a coding block is intra predicted based on right reference samples of the current block, at least one transform block corresponding to the current block is laterally reversed. The laterally reversed at least one transform block is used in reconstructing the current block.

In FIG. 21A, the current block is intra predicted based on a right neighboring sample and an upper neighboring sample. In addition, a size of a transform block 2100 with respect to the current block is equal to a size of the current block. Locations of residual samples included in the transform block 2100 are laterally reversed. For example, a residual sample 2102 located in an upper-left corner of the transform block 2100 is swapped with a residual sample 2116 located in an upper-right corner of the transform block 2100. Other residual samples 2104, 2106, and 2108 located in the left of a first row of the transform block 2100 are respectively swapped with other residual samples 2114, 2112, and 2110 located in the right of the first row of the transform block 2100. With respect to residual samples of remaining rows of the transform block 2100, a residual sample in the left is swapped with a residual sample in the right in a same manner as the first row.

In FIG. 21B, equally as in FIG. 21A, a current block is intra predicted based on a right neighboring sample and an upper neighboring sample. However, the current block is split into four transform blocks. Residual samples of each transform block included in the current block are laterally reversed in a same manner to residual samples of the transform block 2100 of FIG. 21A. For example, a residual sample 2152 located in an upper-left corner of a transform block 2150 is swapped with a residual sample 2158 located in an upper-right corner of the transform block 2150. A residual sample 2154 of the transform block 2150 is swapped with a residual sample 2156 of the transform block 2150. With respect to residual samples of remaining rows of the transform block 2150, a residual sample in the left is swapped with a residual sample in the right in a same manner as the first row. Also, residual samples of other transform blocks 2160, 2170, and 2180 of the current block are laterally reversed in a same manner to residual samples of the transform block 2150.

Hereinafter, an algorithm for a lateral reversal of a transform block will now be described. In the algorithm below, TU_Height and TU_Width respectively refer to a height and width of a transform block. ‘block’ refers to an original transform block, and ResidueBlock refers to a laterally-reversed transform block.

for (Int y=0; y<TU_Height; y++){

for (Int x=0; x<TU_Width; x++){

ResidueBlock [y][x]=block[y][TU_Width−1−x];

}}

According to Equation “ResidueBlock [y][x]=block[y][TU_Width−1−x]”, it is apparent that a transform block is laterally-reversed. A lateral reversal of a transform block may be performed regardless of a size and shape of the transform block.

FIG. 22 illustrates a method of determining a most probable mode (MPM) of a current block, when a right block and a lower-right block of the current block have been decoded prior to the current block. The MPM refers to an intra prediction mode having a high probability to be applied to the current block.

Referring to FIG. 22 , neighboring blocks 2202, 2204, 2206, 2208, 2210, 2212, and 2214 of a current block 2200 are present adjacent to the current block 2200. When the current block 2200 is to be intra predicted, intra prediction modes of the neighboring blocks 2202, 2204, 2206, 2208, 2210, 2212, and 2214 of the current block 2200 are scanned to determine an MPM of the current block 2200. Also, a planar mode, a discrete cosine (DC) mode, a vertical mode, a horizontal mode, a diagonal mode, or the like may be used as a default mode with respect to determining the MPM. Then, an intra prediction mode of the current block 2200 is determined according to the MPM of the current block 2200 and intra prediction information obtained from a bitstream.

The neighboring blocks 2202, 2204, 2206, 2208, 2210, 2212, and 2214 of the current block 2200 may be scanned according to a set order. When some of the neighboring blocks 2202, 2204, 2206, 2208, 2210, 2212, and 2214 have not been decoded or have not been intra predicted, the intra prediction mode is not scanned. Therefore, neighboring blocks whose intra prediction modes cannot be scanned are not used in determining an MPM of a current block.

According to an embodiment, neighboring blocks to be scanned may be limited. For example, intra prediction modes of only the left block 2204, the upper block 2208, and the right block 2212 of the current block 2200 may be scanned to determine the MPM. According to an embodiment, intra prediction modes of the lower-left block 2202, the upper-left block 2206, the upper-right block 2210, and the lower-left block 2202 may be selectively used in determining the MPM.

An order of scanning neighboring blocks may be adaptively changed according to a decoding order of the current block 2200. For example, when the right block 2212 of the current block 2200 has been decoded prior to the current block 2200, an intra prediction mode of the right block 2212 may be scanned prior to an intra prediction mode of the left block 2204. On the other hand, when the right block 2212 of the current block 2200 has not been decoded prior to the current block 2200, the intra prediction mode of the left block 2204 may be scanned prior to the intra prediction mode of the right block 2212. In conclusion, when the right block 2212 of the current block 2200 has been decoded prior to the current block 2200, it is highly probable that the intra prediction mode of the right block 2212 may be used in determining the MPM.

FIG. 23 is a diagram for describing smoothing with respect to reference pixels to be referred to in intra prediction with respect to a current block.

When a current block 2300 is intra predicted, reference pixels adjacent to the current block 2300 are obtained. The obtained reference pixels are smoothed according to variation between the reference pixels. According to the variation between the reference pixels, a strong smoothing filter or a weak smoothing filter may be used. According to an embodiment, for smoothing with respect to a reference pixel, one of at least three smoothing filters may be used according to the variation between the reference pixels.

Factors described below indicate variation between reference pixels.

BilinearLeft=abs (TL+BL−2*L)<threshold

BilinearHalfLeft=abs (TL+L−2*ML)<threshold

BilinearAboveCenter=abs (TL+TR−2*MA)<threshold

BilinearAboveRight=abs (TL+AR−2*T)<threshold

BilinearAboveLeft=abs (AL+TR−2*TL)<threshold

BilinearRight=abs (TR+BR−2*R)<threshold

BilinearHalfRight=abs (TR+R−2*MR)<threshold

BilinearLeft indicates variation of left and lower-left reference samples of a current block. BilinearLeft is determined to be 0 when a value (abs (TL+BL−2*L)) calculated from samples 2302, 2306, and 2308 is less than a threshold value. On the other hand, BilinearLeft is determined to be 1 when the value (abs (TL+BL−2*L)) calculated from the samples 2302, 2306, and 2308 is greater than the threshold value.

BilinearHalfLeft indicates variation of left reference samples of the current block. BilinearHalfLeft is determined to be 0 when a value (abs (TL+L−2*ML)) calculated from samples 2302, 2304, and 2306 is less than a threshold value. On the other hand, BilinearHalfLeft is determined to be 1 when the value (abs (TL+L−2*ML)) calculated from the samples 2302, 2304, and 2306 is greater than the threshold value.

BilinearAboveCenter indicates variation of the left reference samples of the current block. BilinearAboveCenter is determined to be 0 when a value (abs (TL+TR−2*MA)) calculated from samples 2302, 2312, and 2314 is less than a threshold value. On the other hand, BilinearAboveCenter is determined to be 1 when the value (abs (TL+TR−2*MA)) calculated from the samples 2302, 2312, and 2314 is greater than the threshold value.

BilinearAboveRight indicates variation of the left reference samples of the current block. BilinearAboveRight is determined to be 0 when a value (abs (TL+AR−2*T)) calculated from samples 2302, 2314, and 2318 is less than a threshold value. On the other hand, BilinearAboveRight is determined to be 1 when the value (abs (TL+AR−2*T)) calculated from the samples 2302, 2314, and 2318 is greater than the threshold value.

BilinearAboveLeft indicates variation of the left reference samples of the current block. BilinearAboveLeft is determined to be 0 when a value (abs (TL+TR−2*MA)) calculated from samples 2302, 2310, and 2316 is less than a threshold value. On the other hand, BilinearAboveLeft is determined to be 1 when the value (abs (TL+TR−2*MA)) calculated from the samples 2302, 2310, and 2316 is greater than the threshold value.

BilinearRight indicates variation of the right reference samples of the current block. BilinearRight is determined to be 0 when a value (abs (AL+TR−2*TL)) calculated from samples 2316, 2322, and 2324 is less than a threshold value. On the other hand, BilinearRight is determined to be 1 when the value (abs (AL+TR−2*TL)) calculated from the samples 2316, 2322, and 2324 is greater than the threshold value.

BilinearHalfRight indicates variation of the right reference samples of the current block. BilinearHalfRight is determined to be 0 when a value (abs (TR+R−2*MR)) calculated from samples 2316, 2320, and 2322 is less than a threshold value. On the other hand, BilinearHalfRight is determined to be 1 when the value (abs (TR+R−2*MR)) calculated from the samples 2316, 2320, and 2322 is greater than the threshold value.

The threshold value may be randomly determined according to a determined size and intra prediction mode of the current block.

A method of determining whether to apply a strong filter to reference sample filtering according to the variation between the reference samples will now be described based on logical expression below.

1. If Left_available && Right_available{

-   -   If BilinearHalfLeft && BilinearAboveCenter && BilinearHalfRight         Strongfilter=true}

2. If Left_available && !Right_available{

-   -   If BilinearLeft && BilinearAboveRight→Strongfilter=true}

3. If !Left_available && Right_available{

-   -   If BilinearRight && BilinearAboveLeft→Strongfilter=true}

4. If !Left_available && !Right_available→According to weighted difference among AL, TL, MA, T, TR, AR, decide Strongfilter

When both a left block and a right block of the current block 2300 have been decoded, whether to apply the strong filter is determined based on BilinearHalfLeft, BilinearAboveCenter, and BilinearHalfRight. When all of BilinearHalfLeft, BilinearAboveCenter, and BilinearHalfRightrk are 1, reference pixels to be used in prediction with respect to the current block 2300 are smoothed by the strong filter.

When only the left block of the current block 2300 has been decoded, whether to apply the strong filter is determined based on BilinearLeft and BilinearAboveRight. When both BilinearLeft and BilinearAboveRight are 1, reference pixels to be used in prediction with respect to the current block 2300 are smoothed by the strong filter.

When only the right block of the current block 2300 has been decoded, whether to apply the strong filter is determined based on BilinearRight and BilinearAboveLeft. When both BilinearRight and BilinearAboveLeft are 1, reference pixels to be used in prediction with respect to the current block 2300 are smoothed by the strong filter.

When both the left block and the right block of the current block 2300 have not been decoded, whether to apply the strong filter is determined based on a difference between weights of the samples 2302, 2310, 2312, 2314, 2316, and 2318 located in a row adjacent to the current block 2300. For example, when the difference between the weights is greater than a threshold value, the strong filter may be applied.

When the strong filter is applied to filtering with respect to a reference pixel, filtering by a linear interpolation filter is performed on left reference samples, right reference samples, and upper reference samples of the current block 2300. For example, when both the left block and the right block of the current block 2300 have been decoded, a left sample between the sample 2302 and the sample 2306, an upper sample between the sample 2302 and the sample 2316, and a right sample between the sample 2316 and the sample 2322 is used as a reference sample of the current block 2300. Thus, the left sample is filtered based on a result of linear interpolation with respect to the sample 2302 and the sample 2306, the upper sample is filtered based on a result of linear interpolation with respect to the sample 2302 and the sample 2316, and the right sample is filtered based on a result of linear interpolation with respect to the sample 2316 and the sample 2322.

When only the left block of the current block 2300 has been decoded, a left sample between the sample 2302 and the sample 2308, and an upper sample between the sample 2302 and the sample 2318 are used as reference samples of the current block 2300. Thus, the left sample is filtered based on a result of linear interpolation with respect to the sample 2302 and the sample 2308, and the upper sample is filtered based on a result of linear interpolation with respect to the sample 2302 and the sample 2318.

When only the right block of the current block 2300 has been decoded, an upper sample between the sample 2310 and the sample 2316, and a right sample between the sample 2316 and the sample 2324 are used as reference samples of the current block 2300. Thus, the right sample is filtered based on a result of linear interpolation with respect to the sample 2316 and the sample 2324, and the upper sample is filtered based on a result of linear interpolation with respect to the sample 2310 and the sample 2316.

When both the left block and the right block of the current block 2300 have not been decoded, only an upper sample between the sample 2310 and the sample 2318 is a target to be reference sample filtered. Thus, the upper sample is filtered based on a result of linear interpolation with respect to the sample 2310 and the sample 2318.

When the strong filter is not used in smoothing of a reference sample, a weak filter is applied thereto. When the weak filter is applied to smoothing of a reference sample, a 3-tap filter whose filter coefficients are [1,2,1] is applied to left reference samples, right reference samples, and upper reference samples of the current block 2300.

Equation 1 below indicates a method of applying the 3-tap filter. X1 indicates a value of a sample to be filtered, and X1′ indicates a value of a sample that is filtered. X0 and X2 indicate values of samples directly adjacent to both sides of the sample to be filtered. According to Equation 1, samples to be referred to for a current block are filtered.

X1′=(X0+2X1+X2)/4

For example, when the sample 2326 is filtered by using the 3-tap filter, a sample value generated by applying the 3-tap filter to a value of the sample 2326 and values of neighboring samples 2325 and 2327 being directly adjacent thereto is determined to be a filtered value of the sample 2326.

According to an embodiment, when the weak filter is applied to smoothing of a reference sample, a 5-tap filter whose filter coefficients are [2,3,6,3,2] may be applied to reference samples, instead of the 3-tap filter. Alternatively, a filter to be used as the weak filter may be set to be selected from the 3-tap filter and the 5-tap filter.

Equation 2 below indicates a method of applying the 5-tap filter. X2 indicates a value of a sample to be filtered, and X2′ indicates a value of a sample that is filtered. X0, X1, X3, X4 indicate values of samples adjacent to the sample to be filtered within a 2-pixel distance. According to Equation 2, samples to be referred to for a current block are filtered.

X2′=(2X0+3X1+6X2+3X3+2X4)/16

For example, when the sample 2326 is filtered by using the 5-tap filter, a sample value generated by applying the 5-tap filter to a value of the sample 2326 and values of neighboring samples 2316, 2325, 2327, and 2320 within a 2-pixel distance is determined to be a filtered value of the sample 2326.

Filter coefficients of the 3-tap filter and the 5-tap filter may be randomly changed by one of ordinary skill in the art.

FIGS. 24A and 24B illustrate a method of determining a residual block according to horizontal differential pulse-code modulation (DPCM). DPCM is one of data conversion methods, and in which samples are converted by using a difference between values of neighboring samples. In video encoding and decoding, a compression method of a residual block according to frequency-time domain transform and quantization is widely used. However, when sample values of samples of the residual block are uniform, compression efficiency of DPCM transmitting a difference between neighboring sample values may be better than the compression method according to frequency-time domain transform and quantization. In particular, in a case of a directional intra mode of referencing a reference sample in a particular direction, it is highly probable that a sample value of a residual sample located adjacent to the reference sample is small whereas a sample value of a residual signal located distant from the reference sample is large. Therefore, when directions applied to the directional intra mode and DPCM are equal, compression efficiency of DPCM may be better than frequency-time domain transform.

DPCM is divided according to a relative location of a neighboring sample to be referred to for a current sample. For example, in vertical DPCM, a difference between sample values of a current sample and a sample located in a vertical direction with respect to the current sample is used. Also, in horizontal DPCM, a difference between sample values of a current sample and a sample located in a horizontal direction with respect to the current sample is used. In general, when a prediction block corresponding to a residual block has been predicted according to a vertical mode, vertical DPCM may be applied to the residual block. Equally, when a prediction block corresponding to a residual block has been predicted according to a horizontal mode, horizontal DPCM may be applied to the residual block.

In horizontal DPCM, according to whether a right block and a left block of a current prediction block have been decoded prior to the current prediction block, a neighboring sample of a current sample which is to be used in transforming the current sample is determined. When the left block of the current prediction block has been decoded prior to the current prediction block, the current sample is transformed according to a difference between sample values of the current sample and a left sample of the current sample. On the other hand, when the right block of the current prediction block has been decoded prior to the current prediction block, the current sample is transformed according to a difference between sample values of the current sample and a right sample of the current sample.

FIG. 24A illustrates a method of applying DPCM on a current residual block 2400, when a left block of a current prediction block, the left block corresponding to the current residual block 2400, has been decoded prior to the current prediction block.

Samples of the current residual block 2400 are transformed according to horizontal DPCM. In FIG. 24A, because the left block of the current prediction block has been decoded prior to the current prediction block, residual samples of the current residual block 2400 are respectively transformed based on residual samples located in the left. In detail, a new sample value of each residual sample is determined based on a difference between a sample value of a certain residual sample and a sample value of a residual sample located to the directly left of the certain residual sample.

For example, a residual sample 2404 is transformed according to a difference between sample values of the residual sample 2404 and a residual sample 2402. In detail, a new sample value of the residual sample 2404 is determined to be a difference between the sample values of the residual sample 2404 and the residual sample 2402. When the sample value of the residual sample 2402 is 1 and the sample value of the residual sample 2404 is 2, the new sample value of the residual sample 2404 is determined to be 1 that is the difference between the sample values of the residual sample 2404 and the residual sample 2402.

Equally, a residual sample 2406 is transformed according to a difference between sample values of the residual sample 2406 and the residual sample 2404. Also, remaining residual samples of the current residual block 2400 are transformed in a same manner with respect to the residual samples 2404 and 2406.

FIG. 24B illustrates a method of applying DPCM on a current residual block 2450, when a right block of a current prediction block, the right block corresponding to the current residual block 2450, has been decoded prior to the current prediction block.

In FIG. 24B, because the right block of the current prediction block has been decoded prior to the current prediction block, residual samples of the current residual block 2450 are respectively transformed based on residual samples located in the right. In detail, a new sample value of each residual sample is determined based on a difference between a sample value of a certain residual sample and a sample value of a residual sample located to the directly right of the certain residual sample.

For example, a residual sample 2454 is transformed according to a difference between sample values of the residual sample 2454 and a residual sample 2452. In detail, a new sample value of the residual sample 2454 is determined to be a difference between the sample values of the residual sample 2454 and the residual sample 2452. When the sample value of the residual sample 2452 is 1 and the sample value of the residual sample 2454 is 2, the new sample value of the residual sample 2454 is determined to be 1 that is the difference between the sample values of the residual sample 2454 and the residual sample 2452.

Equally, a residual sample 2456 is transformed according to a difference between sample values of the residual sample 2456 and the residual sample 2454. Also, remaining residual samples of the current residual block 2450 are transformed in a same manner with respect to the residual samples 2454 and 2456.

When both the right block and the left block of the current prediction block have been decoded, a direction in which horizontal DPCM is to be applied to the current prediction block may be determined according to whether a directional intra prediction mode applied to the current prediction block is a leftward horizontal mode or a rightward horizontal mode.

FIG. 25 illustrates a range of neighboring samples necessary to determine an illumination coefficient with respect to illumination compensation. The illumination compensation indicates that illumination mismatch between different viewpoints is corrected in a multi-view video. When a dependent viewpoint image is encoded or decoded, the illumination compensation is performed by referring to illumination information of an independent viewpoint image to be referred to for the dependent viewpoint image.

For the illumination compensation, neighboring samples of a current block of the dependent viewpoint image are compared with neighboring samples of a reference block of the independent viewpoint image. As a result of comparing the neighboring samples of the current block with the neighboring samples of the reference block, a compensation coefficient and compensation offsets for the illumination compensation between the current block and the reference block are calculated. Then, a prediction value of the current block is changed according to the compensation coefficient and the compensation offsets for the illumination compensation.

FIG. 25 illustrates a current block 2500 and a reference block 2510. Neighboring samples 2502 of the current block 2500 are located in the left, right, and upper directions of the current block 2500. Equally, neighboring samples 2512 of the reference block 2510 are located in the left, right, and upper directions of the reference block 2510.

Relative locations of the neighboring samples 2502 of the current block 2500 and the neighboring samples 2512 of the reference block 2510 are equal. For example, a neighboring sample 2504 located in the lower right of the current block 2500 corresponds to a neighboring sample 2514 of the reference block 2510. Therefore, the neighboring sample 2504 of the current block 2500 is compared with the neighboring sample 2514 of the reference block 2510. Equally, other neighboring samples of the current block 2500 correspond to other neighboring samples of the reference block 2510 according to relative locations.

In a case where a left block of the current block 2500 has been decoded prior to the current block 2500, a result of comparing neighboring samples 2506 located in the left of the current block 2500 with neighboring samples 2516 located in the left of the reference block 2510 may be used in calculating a compensation coefficient and compensation offsets for illumination compensation. Equally, in a case where a right block of the current block 2500 has been decoded prior to the current block 2500, a result of comparing neighboring samples 2508 located in the right of the current block 2500 with neighboring samples 2518 located in the right of the reference block 2510 may be used in calculating the compensation coefficient and compensation offsets for the illumination compensation.

Therefore, according to whether neighboring blocks of the current block 2500 have been decoded, a range of neighboring samples to be used in the illumination compensation with respect to the current block 2500 is determined.

FIGS. 26A to 26C illustrate a method of predicting a current block according to a position dependent intra prediction combination (PDPC) mode. In the PDPC mode, at least two reference samples required in predicting a current sample are determined according to a location of the current sample. A prediction value of the current sample is determined to be a weighted average value of sample values of the at least two reference samples. Weights to be used in determining the weighted average value are determined according to distances between the current sample and the at least two reference samples.

FIG. 26A illustrates a method of predicting a current block according to a PDPC mode, when only left and upper reference samples of a current block 2600 are available. A prediction value of a sample 2602 is determined to be a weighted average value of sample values of a left reference sample 2604 and an upper reference sample 2606 of the sample 2602. Weights to be applied to the left reference sample 2604 and the upper reference sample 2606 are respectively determined according to a distance between the sample 2602 and the left reference sample 2604 and a distance between the sample 2602 and the upper reference sample 2606.

For example, the weight to be applied to the left reference sample 2604 may be determined in proportion to the distance between the sample 2602 and the upper reference sample 2606. The weight to be applied to the upper reference sample 2606 may be determined in proportion to the distance between the sample 2602 and the left reference sample 2604. Therefore, the weight to be applied to the left reference sample 2604 may be determined to be 2, and the weight to be applied to the upper reference sample 2606 may be determined to be 3. When the sample value of the left reference sample 2604 is 130, and the sample value of the upper reference sample 2606 is 80, the prediction value of the sample 2602 is determined to be 100 that is a weighted average according to the weights ((130×2+80×3)/(2+3)=100).

Residual samples of the current block 2600 are also predicted in a same manner to the sample 2602.

FIG. 26B illustrates a method of predicting a current block according to a PDPC mode, when only right and upper reference samples of a current block 2620 are available. A prediction value of a sample 2622 is determined to be a weighted average value of sample values of a right reference sample 2624 and an upper reference sample 2626 of the sample 2622. Weights to be applied to the right reference sample 2624 and the upper reference sample 2626 are respectively determined according to a distance between the sample 2622 and the right reference sample 2624 and a distance between the sample 2622 and the upper reference sample 2626. Therefore, the left reference sample 2604 of FIG. 26A corresponds to the right reference sample 2624 of FIG. 26B.

For example, the weight to be applied to the right reference sample 2624 may be determined in proportion to the distance between the sample 2622 and the upper reference sample 2626. Also, the weight to be applied to the upper reference sample 2626 may be determined in proportion to the distance between the sample 2622 and the right reference sample 2624. Residual samples of the current block 2620 are also predicted in a same manner to the sample 2622.

FIG. 26C illustrates a method of predicting a current block according to a PDPC mode, when left, right and upper reference samples of a current block 2640 are all available. A prediction value of a sample 2642 is determined to be a weighted average value of sample values of a left reference sample 2644, a right reference sample 2646, and an upper reference sample 2648 of the sample 2642. Weights to be applied to the left reference sample 2644, the right reference sample 2646, and the upper reference sample 2648 are respectively determined according to a distance between the sample 2642 and the left reference sample 2644, a distance between the sample 2642 and the right reference sample 2646, and a distance between the sample 2642 and the upper reference sample 2648.

Alternatively, the prediction value of the sample 2642 may be determined based on a first weighted average value of the left reference sample 2644 and the upper reference sample 2648 and a second weighted average value of the right reference sample 2646 and the upper reference sample 2648, the first weighted average value being obtained in a manner of FIG. 26A and the second weighted average value being obtained in a manner of FIG. 26B. For example, an average value of the first weighted average value and the second weighted average value may be determined to be the prediction value of the sample 2642. As another example, a weighted average value of the first weighted average value and the second weighted average value may be determined to be the prediction value of the sample 2642, based on a weight according to a location of the sample 2642.

The decoder 1640 may predict a current block according to a prediction method determined by the prediction method determiner 1630, and may decode the current block, based on a result of the prediction with respect to the current block.

When split information indicates that the current block is not to be split, the decoder 1640 may obtain, from a bitstream, a final block flag indicating whether the current block is a last block of an encoding tree block including the current block.

When the final block flag indicates that the current block is the last block of the encoding tree block, the decoder 1640 may end decoding of the encoding tree block after the current block is decoded. After the current block is decoded, a next encoding tree block may be decoded by the video decoding device 1600. As in the encoding tree block including the current block, the block splitter 1610, the encoding order determiner 1620, the prediction method determiner 1630, and the block decoder 1640 that are included in the video decoding device 1600 may perform split of a block, determination of an encoding order, and decoding of a final split block on the next encoding tree block.

Also, the decoder 1640 may not obtain the final block flag from the bitstream but may determine whether other blocks except for the current block from among blocks included in the encoding tree block have been decoded, and then may determine whether the current block is the last block of the encoding tree block.

The decoder 1640 may entropy decode a syntax element according to a context of a neighboring block, the syntax element being obtained from the bitstream. For example, a skip flag indicating whether the current block has been encoded according to a skip mode may be entropy encoded according to a context of neighboring blocks of the current block. Therefore, the skip flag may be entropy encoded by referring to a context with respect to whether a right block of the current block has been decoded. Therefore, the syntax element to be entropy encoded with the skip flag according to the context of the neighboring blocks of the current block may be entropy encoded by referring to whether the right block of the current block has been decoded.

According to Equation 3 below, a method of determining context information uiCtx indicating how many neighboring blocks of the current block have been decoded according to the skip mode will now be described. First, an initial value of uiCtx is determined according to whether a left block of the current block has been decoded according to the skip mode. When the left block of the current block has not been decoded according to the skip mode, uiCtx is determined to be 0. On the other hand, when the left block of the current block has been decoded according to the skip mode, uiCtx is determined to be 1. When an upper block of the current block has been decoded according to the skip mode, uiCtx is increased by 1. Also, when the right block of the current block has been decoded according to the skip mode, uiCtx is increased by 1. Therefore, uiCtx may indicate a value from among 0 to 3. According to an embodiment, a maximum value of uiCtx may be limited to 2.

uiCtx=left is skip 1:0

uiCtx+=above is skip? 1:0

uiCtx+=right is skip? 1:0

uiCtx or min(uiCtx,2)   [Equation 3]

The skip flag is entropy decoded according to context-based probability information indicated by uiCtx determined according to Equation 3.

The decoder 1640 may entropy decode split information and split shape information obtained from a bitstream, according to the context of the neighboring blocks. The split information indicates whether the current block is to be split, and the split shape information indicates to which shape the current block is to be split. The split information may be entropy decoded according to whether the neighboring blocks of the current block, the neighboring blocks including the left block, the upper block, and the right block, have been split, and the split shape information may be entropy decoded according to which shape the neighboring blocks of the current block, the neighboring blocks including the left block, the upper block, and the right block, have been split.

According to Equation 4 below, a method of determining context information uiCtx indicating how many neighboring blocks of the current block have been split will now be described. First, an initial value of uiCtx is determined according to whether the left block of the current block has been split. When the left block of the current block has not been split, uiCtx is determined to be 0. On the other hand, when the left block of the current block has been split, uiCtx is determined to be 1. When the upper block of the current block has been split, uiCtx is increased by 1. Also, when the right block of the current block has been split, uiCtx is increased by 1. Therefore, uiCtx may indicate a value from among 0 to 3. According to an embodiment, a maximum value of uiCtx may be limited to 2.

uiCtx=left_Depth>curr_Depth? 1:0

uiCtx+=above_Depth>curr_Depth? 1:0

uiCtx+=right_Depth>curr_Depth? 1:0

uiCtx or min(uiCtx,2)   [Equation 4]

The split information is entropy decoded according to context-based probability information indicated by uiCtx determined according to Equation 4.

The decoder 1640 may entropy decode FRUC merge information and FRUC motion prediction information obtained from a bitstream, according to the context of the neighboring blocks. The FRUC merge information indicates whether the current block is to be predicted according to a FRUC merge mode, and the FRUC motion prediction information indicates whether the current block is to be predicted according to a FRUC motion prediction mode. The FRUC merge information may be entropy decoded according to whether the neighboring blocks of the current block, the neighboring blocks including the left block, the upper block, and the right block, have been predicted according to the FRUC merge mode, and the FRUC motion prediction information may be entropy decoded according to whether the neighboring blocks of the current block, the neighboring blocks including the left block, the upper block, and the right block, have been predicted according to the FRUC motion prediction mode.

According to Equation 5 below, a method of determining context information uiCtx indicating how many neighboring blocks of the current block have been decoded according to the FRUC merge mode will now be described. First, an initial value of uiCtx is determined according to whether the left block of the current block has been decoded according to the FRUC merge mode. When the left block of the current block has not been decoded according to the FRUC merge mode, uiCtx is determined to be 0. On the other hand, when the left block of the current block has been decoded according to the FRUC merge mode, uiCtx is determined to be 1. When the upper block of the current block has been decoded according to the FRUC merge mode, uiCtx is increased by 1. Also, when the right block of the current block has been decoded according to the FRUC merge mode, uiCtx is increased by 1. Therefore, uiCtx may indicate a value from among 0 to 3. According to an embodiment, a maximum value of uiCtx may be limited to 2.

uiCtx=left is FRUCmergeMode? 1:0

uiCtx+=above is FRUCmergeMode? 1:0

uiCtx+=right is FRUCmergeMode? 1:0

uiCtx or min(uiCtx,2)   [Equation 5]

The FRUC merge information is entropy decoded according to context-based probability information indicated by uiCtx determined according to Equation 5.

According to Equation 6 below, a method of determining context information uiCtx indicating how many neighboring blocks of the current block have been decoded according to the FRUC motion prediction mode will now be described. First, an initial value of uiCtx is determined according to whether the left block of the current block has been decoded according to the FRUC motion prediction mode. When the left block of the current block has not been decoded according to the FRUC motion prediction mode, uiCtx is determined to be 0. On the other hand, when the left block of the current block has been decoded according to the FRUC motion prediction mode, uiCtx is determined to be 1. When the upper block of the current block has been decoded according to the FRUC motion prediction mode, uiCtx is increased by 1. Also, when the right block of the current block has been decoded according to the FRUC motion prediction mode, uiCtx is increased by 1. Therefore, uiCtx may indicate a value from among 0 to 3. According to an embodiment, a maximum value of uiCtx may be limited to 2.

uiCtx=left FRUCmergeMode==FRUC_MERGE_BILATERALMV? 1:0

uiCtx+=above FRUCmergeMode==FRUC_MERGE_BILATERALMV? 1:0

uiCtx+=right FRUCmergeMode==FRUC_MERGE_BILATERALMV? 1:0

uiCtx or min(uiCtx,2)   [Equation 6]

The FRUC motion prediction information is entropy decoded according to context-based probability information indicated by uiCtx determined according to Equation 6.

The decoder 1640 may entropy decode affine mode information obtained from a bitstream, according to the context of the neighboring blocks. The affine mode information may be entropy decoded according to whether the neighboring blocks of the current block, the neighboring blocks including the left block, the upper block, and the right block, have been predicted according to an affine mode.

According to Equation 7 below, a method of determining context information uiCtx indicating how many neighboring blocks of the current block have been decoded according to the affine mode will now be described. First, an initial value of uiCtx is determined according to whether the left block of the current block has been decoded according to the affine mode. When the left block of the current block has not been decoded according to the affine mode, uiCtx is determined to be 0. On the other hand, when the left block of the current block has been decoded according to the affine mode, uiCtx is determined to be 1. When the upper block of the current block has been decoded according to the affine mode, uiCtx is increased by 1. Also, when the right block of the current block has been decoded according to the affine mode, uiCtx is increased by 1. Therefore, uiCtx may indicate a value from among 0 to 3. According to an embodiment, a maximum value of uiCtx may be limited to 2.

uiCtx=left is Affine? 1:0

uiCtx+=above is Affine? 1:0

uiCtx+=right is Affine? 1:0

uiCtx or min(uiCtx,2)   [Equation 7]

The affine mode information is entropy decoded according to context-based probability information indicated by uiCtx determined according to Equation 7.

The decoder 1640 may entropy decode motion vector resolution information obtained from a bitstream, according to the context of the neighboring blocks. The motion vector resolution information indicates whether a motion vector resolution of the current block is a default motion vector resolution. For example, when the motion vector resolution is the default motion vector resolution, the motion vector resolution information may indicate 0, and when the motion vector resolution is not the default motion vector resolution, the motion vector resolution information may indicate 1. The motion vector resolution information may be entropy decoded according to which motion vector resolution the neighboring blocks of the current block, the neighboring blocks including the left block, the upper block, and the right block, have been predicted.

According to Equation 8 below, a method of determining context information uiCtx indicating whether the neighboring blocks of the current block have been decoded according to the default motion vector resolution will now be described. First, an initial value of uiCtx is determined according to whether the left block of the current block has been decoded according to the default motion vector resolution. When the left block of the current block has not been decoded according to the default motion vector resolution, uiCtx is determined to be 0. On the other hand, when the left block of the current block has been decoded according to the default motion vector resolution, uiCtx is determined to be 1. When the left block of the current block has not been decoded according to the default motion vector resolution, uiCtx is increased by 1. Also, when the right block of the current block has not been decoded according to the default motion vector resolution, uiCtx is increased by 1. Therefore, uiCtx may indicate a value from among 0 to 3. According to an embodiment, a maximum value of uiCtx may be limited to 2.

uiCtx=left MVresFlag>? 1:0

uiCtx+=above MVresFlag>? 1:0

uiCtx+=right MVresFlag>? 1:0

uiCtx or min(uiCtx,2)   [Equation 8]

The motion vector resolution information is entropy decoded according to context-based probability information indicated by uiCtx determined according to Equation 8.

Therefore, the decoder 1640 may entropy decode syntax elements by referring to whether the right block of the current block has been decoded, the syntax elements being entropy decoded according to the context of the neighboring block. Equally, other syntax elements that are not described in the present specification may be entropy decoded based on the right block of the current block.

The decoder 1640 may inverse quantize and inverse transform residual data obtained from the bitstream. Then, the decoder 1640 may reconstruct the current block by using the inverse quantized and inverse transformed residual data and the prediction result about the current block.

FIG. 27 illustrates a video decoding method according to an embodiment involving splitting a current block and determining an encoding order of split lower blocks.

In operation 2710, split information indicating whether a current block is to be split is obtained from a bitstream.

In operation 2720, when the split information indicates that the current block is not to be split, the current block is decoded based on encoding information about the current block.

When the current block is not split based on the split information but is inter predicted, reference samples to be referred to for the current block are determined according to whether a left block and a right block of the current block have been decoded. Then, the current block is predicted and decoded based on the reference samples.

When only the left block of the current block has been decoded, samples adjacent to the current block in left and upper directions are included in the reference samples. When only the right block of the current block has been decoded, samples adjacent to the current block in right and upper directions are included in the reference samples. When both the left and right blocks of the current block have been decoded, samples adjacent to the current block in right, left and upper directions are included in the reference samples. When both the left and right blocks of the current block have not been decoded, samples adjacent to the current block in an upper direction are included in the reference samples.

When the current block is not split based on the split information but is intra predicted, a plurality of most-frequent intra prediction modes of the current block may be determined. In a case where the left block of the current block has been decoded prior to the current block by using an intra prediction method, a most-frequent intra prediction mode of the current block may be determined by referring to an intra prediction mode of the left block of the current block. Equally, when the right block of the current block has been decoded prior to the current block by using the intra prediction method, the most-frequent intra prediction mode of the current block may be determined by referring to an intra prediction mode of the right block of the current block

When the current block is not split based on the split information but is intra predicted, reference samples to be used in intra prediction with respect to the current block are obtained. When the left block of the current block has been decoded prior to the current block, a reference sample may be obtained from the left block of the current block. Equally, when the right block of the current block has been decoded prior to the current block, a reference sample may be obtained from the right block of the current block.

When the current block is inter predicted, it is checked whether the right block of the current block has been decoded according to inter prediction. When the right block of the current block has been decoded according to inter prediction, a motion vector of the current block is determined by using a motion vector of the right block.

When the current block is inter predicted according to the merge mode, motion vector candidates are obtained from a right block, a lower-right block, an upper block, an upper-left block, a left block, and an upper-right block of the current block. When the current block is inter predicted according to an AMVP mode, a first motion vector candidate is determined from the right block or the lower-right block of the current block, and a second motion vector candidate is determined from the upper block, the upper-right block, or the upper-left block of the current block.

When the current block is inter predicted according to the AMVP mode, and the right block of the current block has been decoded prior to the current block, a first motion vector candidate may be determined from the right block or the lower-right block of the current block, and a second motion vector candidate may be determined from the upper block, the upper-right block, or the upper-left block of the current block.

After prediction is performed on the current block, a transform block corresponding to the current block may be determined according to a result of inverse quantizing and inverse transforming residual data. Then, the current block may be reconstructed according to the inverse quantized and inverse transformed residual data of the transform block.

To correct an illumination mismatch between different viewpoints in a multi-view video, prediction values of the current block may be illumination compensated for based on illumination information obtained from neighboring samples of the current block and neighboring samples of a reference block.

When the left block of the current block has been decoded prior to the current block, the illumination information is obtained from left-neighboring samples of the current block and left-neighboring samples of the reference block. When the right block of the current block has been decoded prior to the current block, the illumination information is obtained from right-neighboring samples of the current block and right-neighboring samples of the reference block.

When the current block is intra predicted according to a location-based intra prediction mode, a current sample included in the current block is predicted according to a vertical location and a vertical reference sample and a horizontal location and a horizontal reference sample of the current sample.

When the left block of the current block has been decoded prior to the current block, the horizontal reference sample is located at a crosspoint of a row where the current sample is located and a column adjacent to the current block in a left direction, and the horizontal location is determined based on a distance between the current sample and the horizontal reference sample.

Equally, when the right block of the current block has been decoded prior to the current block, the horizontal reference sample is located at a crosspoint of a row where the current sample is located and a column adjacent to the current block in a right direction, and the horizontal location is determined based on a distance between the current sample and the horizontal reference sample.

In a case where the current block is intra predicted, the left block of the current block has not been decoded prior to the current block, and the right block of the current block has been decoded prior to the current block, inverse quantized and inverse transformed residual data may be left-right flipped and thus may be used in reconstructing the current block.

When the transform block is determined according to a DPCM mode, residual data is not inverse transformed according to frequency-time domain transform but is inverse transformed according to the DPCM mode. According to the DPCM mode, a residual value of the current sample of the transform block is re-calculated based on a neighboring sample from among the neighboring samples of the current sample. Then, the transform block is determined based on the re-calculated residual value of the current sample.

When the transform block is determined according to a horizontal DPCM mode, it is determined, according to whether the neighboring blocks of the current block have been decoded, which neighboring sample is used in re-calculating a residual value of the current sample. When the left block of the current block has been decoded prior to the current block, a left sample of the current sample is determined as a neighboring sample to be used in re-calculation. Equally, when the right block of the current block has been decoded prior to the current block, a right sample of the current sample is determined as a neighboring sample to be used in the re-calculation.

In operation 2730, when the split information indicates that the current block is to be split, the current block is split into at least two lower blocks, encoding order information indicating an encoding order of the lower blocks of the current block is obtained from the bitstream, a decoding order of the lower blocks is determined based on the encoding order information, and the lower blocks are decoded according to the decoding order.

In operations 2710 to 2730, a plurality of pieces of information obtained from the bitstream are entropy decoded and thus are used in decoding an image. When the left block of the current block has been decoded prior to the current block, entropy decoding with respect to the information may be performed based on context information of the left block of the current block. Equally, when the right block of the current block has been decoded prior to the current block, entropy decoding with respect to the information may be performed based on context information of the right block of the current block.

Functions of the video decoding device 1600 which are described with reference to FIG. 16 may be included in the video decoding method 2700.

FIG. 28 illustrates a video encoding device 2800 according to an embodiment involving splitting a current block and determining an encoding order of split lower blocks.

The video encoding device 2800 includes an encoding information generator 2810 and an output unit 2820. In FIG. 28 , the encoding information generator 2810 and the output unit 2820 are illustrated as separate configuring units, but in another embodiment, the encoding information generator 2810 and the output unit 2820 may be combined to be implemented as one configuring unit.

In FIG. 28 , the encoding information generator 2810 and the output unit 2820 are illustrated as configuring units included in one device, but devices performing respective functions of the encoding information generator 2810 and the output unit 2820 are not required to be physically adjacent to each other. Therefore, in another embodiment, the encoding information generator 2810 and the output unit 2820 may be dispersed.

The encoding information generator 2810 and the output unit 2820 may be implemented by one processor according to an embodiment. Alternatively, they may be implemented by a plurality of processors according to another embodiment.

Functions performed by the encoding information generator 2810 and the output unit 2820 of FIG. 32 may be performed by the output unit 130 of FIG. 1A.

The encoding information generator 2810 may split a current block into at least two lower blocks, and according to a result of the split of the current block, may determine whether to split the current block. For example, when coding efficiency by splitting the current block is good, the encoding information generator 2810 may determine to split the current block, and when coding efficiency by not splitting the current block is good, the encoding information generator 2810 may determine not to split the current block.

The encoding information generator 2810 may generate split information indicating whether the current block is to be split. Then, the encoding information generator 2810 may determine a split method for the current block according to the coding efficiency, and may generate split shape information indicating the split method for the current block.

The encoding information generator 2810 may determine an encoding order of lower blocks included in the current block, based on coding efficiency according to the encoding order, and may generate encoding order information indicating the encoding order of the lower blocks.

When the current block is not to be further encoded, the encoding information generator 2810 may determine a prediction mode with respect to the current block. The encoding information generator 2810 may determine the prediction mode with respect to the current block, according to coding efficiencies of prediction modes that are applicable to the current block. The prediction modes that are applicable to the current block may include a directional mode, a DC mode, a planar mode, a MPI mode, an LM chroma mode, an MPC mode, a merge mode, an AMVP mode, an OBMC mode, a sub-block MVP mode, an affine merge mode, an affine AMVP mode, a bilateral matching FRUC mode, a template matching FRUC mode, a PDPC mode, or the like.

The output unit 2820 outputs a bitstream including encoding information about the current block, the encoding information being generated by the encoding information generator 2810. The encoding information about the current block may include split information, split shape information, split order information, prediction mode information, or the like.

The video encoding device 2800 of FIG. 28 may perform a video encoding method corresponding to the video decoding method 2700 performed by the video decoding device 1600 of FIG. 16 .

FIG. 29 illustrates a video encoding method according to an embodiment involving splitting a current block and determining an encoding order of split lower blocks.

In operation 2910, a current block is split into at least two lower blocks.

In operation 2920, according to a result of splitting the current block, whether to split the current block is determined, and split information indicating whether to split the current block is generated.

In operation 2930, according to coding efficiency of the current block, an encoding order of the lower blocks of the current block is determined, and encoding order information indicating the encoding order of the lower blocks is generated.

In operation 2940, a bitstream including split information and the encoding order information is output.

Functions of the video encoding device 2800 which are described with reference to FIG. 28 may be included in the video encoding method.

According to the video encoding technique based on coding units having a tree structure which is described with reference to FIGS. 1 to 29 , image data of a spatial domain is encoded in each of the coding units having a tree structure, and decoding is performed on each largest coding unit according to the video decoding technique based on coding units having a tree structure so that the image data of the spatial domain is reconstructed, and by doing so, a picture and a video that is a picture sequence may be reconstructed. The reconstructed video may be reproduced by a reproducing apparatus, may be stored in a storage medium, or may be transmitted through a network.

The embodiments according to the present disclosure may be written as computer programs and may be implemented in a general-use digital computer that executes the programs by using a computer-readable recording medium.

While the best embodiments of the present disclosure have been described, it will be understood by one of ordinary skill in the art that various replacements, modifications, or changes with respect to the present disclosure may be made therein without departing from the spirit and scope as defined by the following claims. That is, the claims will be construed as including the various replacements, modifications, or changes with respect to the present disclosure. Therefore, the descriptions provided in the specification and drawings should be considered in a descriptive sense only and not for purposes of limitation. 

1. A video decoding method comprising: obtaining, from a bitstream, encoding order information indicating a decoding order of at least two coding units split from a current coding unit, the at least two coding units including horizontally neighboring coding units; determining whether the decoding order of the at least two coding units is a first order from a left coding unit to a right coding unit, among the horizontally neighboring coding units, or a second order from the right coding unit to the left coding unit, based on the encoding order information; and decoding the horizontally neighboring coding units according to the first order or the second order, wherein the decoding of the horizontally neighboring coding units comprises: when the right coding unit is decoded prior to the left coding unit, among the horizontally neighboring coding units, determining a context model for the left coding unit based on whether a width or a height of the right coding unit is greater than a width or a height of the left coding unit; obtaining, from the bitstream, split information of the left coding unit, by performing entropy decoding using the context model; and when the split information indicates a split of the left coding unit, splitting the left coding unit into two or three coding units, vertically or horizontally; and when the split information indicates a non-split of the left coding unit, decoding the left coding unit.
 2. A video decoding device comprising: an encoding order determiner configured to obtain, from a bitstream, encoding order information indicating a decoding order of at least two coding units split from a current coding unit, the at least two coding units including horizontally neighboring coding units, and determine whether the decoding order of the at least two coding units is a first order from a left coding unit to a right coding unit, among the horizontally neighboring coding units, or a second order from the right coding unit to the left coding unit, based on the encoding order information; and a decoder configured to decode the horizontally neighboring coding units according to the first order or the second order, characterized in that: when the right coding unit is decoded prior to the left coding unit, among the horizontally neighboring coding units, according to the second order, the decoder determines a context model for the left coding unit based on whether a width or a height of the right coding unit is greater than a width or a height of the left coding unit, and obtains, from the bitstream, split information of the left coding unit, by performing entropy decoding using the context model, when the split information indicates a split of the left coding unit, the decoder splits the left coding unit into two or three coding units, vertically or horizontally, and when the split information indicates a non-split of the left coding unit, the decoder decodes the left coding unit.
 3. A video encoding method comprising: determining an encoding order of horizontally neighboring lower coding units, among at least two coding units split from a current coding unit, the at least two coding units including horizontally neighboring coding units; generating encoding order information indicating whether the encoding order of the horizontally neighboring coding units is a first order from a left coding unit to a right coding unit, among the horizontally neighboring coding units, or a second order from the right coding unit to the left coding unit; when the right coding unit is coded prior to the left coding unit, among the horizontally neighboring coding units, according to the second order, determining a context model for the left coding unit based on whether a width or a height of the right coding unit is greater than a width or a height of the left coding unit; performing entropy coding on split information of the left coding unit by using the context model, the split information indicating whether the left coding unit is split into two or three coding units vertically or horizontally, or not split into smaller coding units; and outputting a bitstream comprising the encoding order information and the split information of the left coding unit. 